Metamath Proof Explorer Home Metamath Proof Explorer
Most Recent Proofs 		 
Mirrors  >  Home  >  MPE Home  >  Th. List  >  Recent ILE Most Recent             Other  >  MM 100
Most recent proofs    These are the 100 (Unicode, GIF) or 1000 (Unicode, GIF) most recent proofs in the set.mm database for the Metamath Proof Explorer (and the Hilbert Space Explorer). The set.mm database is maintained on GitHub with master (stable) and develop (development) versions. This page was created from develop commit 212ee7d9, also available here: set.mm (43MB) or set.mm.bz2 (compressed, 13MB).

The original proofs of theorems with recently shortened proofs can often be found by appending "OLD" to the theorem name, for example 19.43OLD for 19.43. The "OLD" versions are usually deleted after a year.

Other links    Contact us.    Mailing list: Metamath Google Group Updated 7-Dec-2021 .    Contributing: How can I contribute to Metamath?    Syndication: RSS feed (courtesy of Dan Getz)    Related wikis: Ghilbert Google Group.

Recent news items    (15-Nov-2025) Thierry Arnoux added a new proof to the 100 theorem list, The Impossibility of Trisecting the Angle and Doubling the Cube, trisecnconstr and 2sqr3nconstr.

(7-Aug-2021) Version 0.198 of the metamath program fixes a bug in "write source ... /rewrap" that prevented end-of-sentence punctuation from appearing in column 79, causing some rewrapped lines to be shorter than necessary. Because this affects about 2000 lines in set.mm, you should use version 0.198 or later for rewrapping before submitting to GitHub.

(7-May-2021) Mario Carneiro has written a Metamath verifier in Lean.

(5-May-2021) Marnix Klooster has written a Metamath verifier in Zig.

(24-Mar-2021) Metamath was mentioned in a couple of articles about OpenAI: Researchers find that large language models struggle with math and What Is GPT-F?.

(26-Dec-2020) Version 0.194 of the metamath program adds the keyword "htmlexturl" to the $t comment to specify external versions of theorem pages. This keyward has been added to set.mm, and you must update your local copy of set.mm for "verify markup" to pass with the new program version.

(19-Dec-2020) Aleksandr A. Adamov has translated the Wikipedia Metamath page into Russian.

(19-Nov-2020) Eric Schmidt's checkmm.cpp was used as a test case for C'est, "a non-standard version of the C++20 standard library, with enhanced support for compile-time evaluation." See C++20 Compile-time Metamath Proof Verification using C'est.

(10-Nov-2020) Filip Cernatescu has updated the XPuzzle (Android app) to version 1.2. XPuzzle is a puzzle with math formulas derived from the Metamath system. At the bottom of the web page is a link to the Google Play Store, where the app can be found.

(7-Nov-2020) Richard Penner created a cross-reference guide between Frege's logic notation and the notation used by set.mm.

(4-Sep-2020) Version 0.192 of the metamath program adds the qualifier '/extract' to 'write source'. See 'help write source' and also this Google Group post.

(23-Aug-2020) Version 0.188 of the metamath program adds keywords Conclusion, Fact, Introduction, Paragraph, Scolia, Scolion, Subsection, and Table to bibliographic references. See 'help write bibliography' for the complete current list.

   Older news...

Color key:   Metamath Proof Explorer  Metamath Proof Explorer   Hilbert Space Explorer  Hilbert Space Explorer   User Mathboxes  User Mathboxes  

Last updated on 29-Sep-2026 at 5:30 AM ET.
Recent Additions to the Metamath Proof Explorer   Notes (last updated 7-Dec-2020 )
DateLabelDescription
Theorem
 
27-Sep-2026elhf 9888 Membership in the hereditarily finite sets. (Contributed by Scott Fenton, 9-Jul-2015.) Reduce axiom usage and shorten proof. (Revised by BJ, 27-Sep-2026.)
(𝐴 ∈ HF ↔ ∃𝑥 ∈ ω 𝐴 ∈ (𝑅1‘𝑥))
 
27-Sep-2026r1dmlim 9756 The domain of the cumulative hierarchy of sets function is a limit ordinal. This weak form of r1fnon 9757 avoids ax-rep 5232. (Contributed by Mario Carneiro, 16-Nov-2014.) Extract this statement from its conjunction with r1fun 9755. (Revised by BJ, 27-Sep-2026.)
Lim dom 𝑅1
 
27-Sep-2026r1fun 9755 The cumulative hierarchy of sets function is a function. (Contributed by Mario Carneiro, 16-Nov-2014.) Extract this statement from its conjunction with r1dmlim 9756. (Revised by BJ, 27-Sep-2026.)
Fun 𝑅1
 
26-Sep-2026omsshf 45974 The class of finite ordinals is included in the class of hereditarily finite sets. (Contributed by Eric Schmidt, 26-Sep-2026.)
ω ⊆ HF
 
26-Sep-2026omhf 45973 Finite ordinals are hereditarily finite sets. (Contributed by Eric Schmidt, 26-Sep-2026.)
(𝐴 ∈ ω → 𝐴 ∈ HF )
 
26-Sep-2026hfrel 45972 A relation is a hereditarily finite set iff its domain and range are. (Contributed by Eric Schmidt, 26-Sep-2026.)
(Rel 𝑅 → (𝑅 ∈ HF ↔ (dom 𝑅 ∈ HF ∧ ran 𝑅 ∈ HF )))
 
26-Sep-2026hfrn 45971 The range of a hereditarily finite set is hereditarily finite. (Contributed by Eric Schmidt, 26-Sep-2026.)
(𝐴 ∈ HF → ran 𝐴 ∈ HF )
 
26-Sep-2026hfdm 45970 The domain of a hereditarily finite set is hereditarily finite. (Contributed by Eric Schmidt, 26-Sep-2026.)
(𝐴 ∈ HF → dom 𝐴 ∈ HF )
 
26-Sep-2026hfxp 45969 The Cartesian product of two hereditarily finite sets is a hereditarily finite set. (Contributed by Eric Schmidt, 26-Sep-2026.)
((𝐴 ∈ HF ∧ 𝐵 ∈ HF ) → (𝐴 × 𝐵) ∈ HF )
 
26-Sep-2026hfpr 45968 A pair whose members are hereditarily finite sets is a hereditarily finite set. (Contributed by Eric Schmidt, 26-Sep-2026.)
((𝐴 ∈ HF ∧ 𝐵 ∈ HF ) → {𝐴, 𝐵} ∈ HF )
 
24-Sep-2026hftsk 10845 The set of hereditarily finite sets is a Tarski class. (The Tarski-Grothendieck Axiom is not needed for this theorem.) (Contributed by Mario Carneiro, 28-May-2013.) Restate using the defined HF symbol. (Revised by Eric Schmidt, 24-Sep-2026.)
HF ∈ Tarski
 
24-Sep-2026hfomALT 10842 Alternate proof of hfom 10302, shorter as a consequence of inar1 10841, but requiring AC. (Contributed by Mario Carneiro, 27-May-2013.) Restate using the defined HF symbol. (Revised by Eric Schmidt, 24-Sep-2026.) (Proof modification is discouraged.) (New usage is discouraged.)
HF ≈ ω
 
24-Sep-2026tskhf 10834 A nonempty Tarski class contains the whole finite cumulative hierarchy. (This proof does not use ax-inf 9623.) (Contributed by NM, 22-Feb-2011.) Restate using the defined HF symbol. (Revised by Eric Schmidt, 24-Sep-2026.)
((𝑇 ∈ Tarski ∧ 𝑇 ≠ ∅) → HF ⊆ 𝑇)
 
24-Sep-2026hfom 10302 The set of hereditarily finite sets is countable. See ackbij2 10301 for an explicit bijection that works without Infinity. See also hfomALT 10842. (Contributed by Stefan O'Rear, 18-Nov-2014.) Restate using the defined HF symbol. (Revised by Eric Schmidt, 24-Sep-2026.)
HF ≈ ω
 
24-Sep-2026ackbij2 10301 The Ackermann bijection, part 2: hereditarily finite sets can be represented by recursive binary notation. (Contributed by Stefan O'Rear, 18-Nov-2014.) Restate using the defined HF symbol. (Revised by Eric Schmidt, 24-Sep-2026.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘∪ 𝑦 ∈ 𝑥 ({𝑦} × 𝒫 𝑦)))    &   𝐺 = (𝑥 ∈ V ↦ (𝑦 ∈ 𝒫 dom 𝑥 ↦ (𝐹‘(𝑥 “ 𝑦))))    &   𝐻 = ∪ (rec(𝐺, ∅) “ ω)    ⇒   𝐻: HF –1-1-onto→ω
 
24-Sep-2026dfhf2 9887 Alternate definition of the class of hereditarily finite sets as the value of the cumulative hierarchy of sets function at ω. This characterization is simpler but requires the axiom of infinity to hold. (Contributed by BTernaryTau, 25-Jan-2026.) Restate using the defined HF symbol. (Revised by Eric Schmidt, 24-Sep-2026.)
HF = (𝑅1‘ω)
 
17-Sep-2026hfpw 9907 The power class of a hereditarily finite set is hereditarily finite. (Contributed by Scott Fenton, 16-Jul-2015.) Avoid ax-reg 9570, ax-inf2 9626. (Revised by BTernaryTau, 17-Sep-2026.)
(𝐴 ∈ HF → 𝒫 𝐴 ∈ HF )
 
17-Sep-2026hfuni 9905 The union of a hereditarily finite set is hereditarily finite. (Contributed by Scott Fenton, 16-Jul-2015.) Avoid ax-reg 9570, ax-inf2 9626. (Revised by BTernaryTau, 17-Sep-2026.)
(𝐴 ∈ HF → ∪ 𝐴 ∈ HF )
 
17-Sep-2026hfsn 9901 The singleton of a hereditarily finite set is a hereditarily finite set. (Contributed by Scott Fenton, 15-Jul-2015.) Avoid ax-reg 9570, ax-inf2 9626. (Revised by BTernaryTau, 17-Sep-2026.)
(𝐴 ∈ HF → {𝐴} ∈ HF )
 
17-Sep-2026hfun 9899 The union of two hereditarily finite sets is a hereditarily finite set. (Contributed by Scott Fenton, 15-Jul-2015.) Avoid ax-reg 9570, ax-inf2 9626. (Revised by BTernaryTau, 17-Sep-2026.)
((𝐴 ∈ HF ∧ 𝐵 ∈ HF ) → (𝐴 ∪ 𝐵) ∈ HF )
 
17-Sep-2026hfsshf 9896 Any subset of a hereditarily finite set is itself a hereditarily finite set. (Contributed by BTernaryTau, 17-Sep-2026.)
((𝐴 ⊆ 𝐵 ∧ 𝐵 ∈ HF ) → 𝐴 ∈ HF )
 
17-Sep-2026hfelhf 9895 Any member of a hereditarily finite set is itself a hereditarily finite set. (Contributed by Scott Fenton, 16-Jul-2015.) Avoid ax-reg 9570, ax-inf2 9626. (Revised by BTernaryTau, 17-Sep-2026.)
((𝐴 ∈ 𝐵 ∧ 𝐵 ∈ HF ) → 𝐴 ∈ HF )
 
17-Sep-2026elhf3 9894 A set is hereditarily finite if and only if it is finite and all its members are hereditarily finite. (Contributed by Eric Schmidt, 8-Sep-2026.) Avoid ax-reg 9570, ax-inf2 9626. (Revised by BTernaryTau, 17-Sep-2026.)
(𝐴 ∈ HF ↔ (𝐴 ∈ Fin ∧ 𝐴 ⊆ HF ))
 
17-Sep-2026elhf4 9893 A set is hereditarily finite iff it is finite and all of its elements are hereditarily finite. (Contributed by BTernaryTau, 19-Jan-2026.) Use HF. (Revised by BTernaryTau, 17-Sep-2026.)
(𝐴 ∈ HF ↔ (𝐴 ∈ Fin ∧ ∀𝑥 ∈ 𝐴 𝑥 ∈ HF ))
 
16-Sep-2026dvdssqnn 16721 Two positive integers are divisible iff their squares are. (Contributed by Scott Fenton, 18-Apr-2014.) (Revised by Mario Carneiro, 19-Apr-2014.) (Proof shortened by AV, 16-Sep-2026.)
((𝑀 ∈ ℕ ∧ 𝑁 ∈ ℕ) → (𝑀 ∥ 𝑁 ↔ (𝑀↑2) ∥ (𝑁↑2)))
 
15-Sep-2026fltoprmgt3 27978 Fermat's last theorem holds for any exponent greater than 2 if it holds for all odd prime exponents greater than 3. (TODO-AV: after a proof is available for 𝑁 = 3, see flt3, the hypothesis fltoprmgt3.3 can be removed.) (Contributed by AV, 15-Sep-2026.)
(𝜑 → 𝐴 ∈ ℕ)    &   (𝜑 → 𝐵 ∈ ℕ)    &   (𝜑 → 𝐶 ∈ ℕ)    &   (𝜑 → 𝑁 ∈ (ℤ≥‘3))    &   (𝜑 → ∀𝑎 ∈ ℕ ∀𝑏 ∈ ℕ ∀𝑐 ∈ ℕ ∀𝑝 ∈ ℙ (3 < 𝑝 → ((𝑎↑𝑝) + (𝑏↑𝑝)) ≠ (𝑐↑𝑝)))    &   (𝜑 → ((𝑎↑3) + (𝑏↑3)) ≠ (𝑐↑3))    ⇒   (𝜑 → ((𝐴↑𝑁) + (𝐵↑𝑁)) ≠ (𝐶↑𝑁))
 
15-Sep-2026fltoprm 27977 Fermat's last theorem holds for any exponent greater than 2 if it holds for odd prime exponents. (Contributed by AV, 15-Sep-2026.)
(𝜑 → 𝐴 ∈ ℕ)    &   (𝜑 → 𝐵 ∈ ℕ)    &   (𝜑 → 𝐶 ∈ ℕ)    &   (𝜑 → 𝑁 ∈ (ℤ≥‘3))    &   (𝜑 → ∀𝑎 ∈ ℕ ∀𝑏 ∈ ℕ ∀𝑐 ∈ ℕ ∀𝑝 ∈ ℙ (2 < 𝑝 → ((𝑎↑𝑝) + (𝑏↑𝑝)) ≠ (𝑐↑𝑝)))    ⇒   (𝜑 → ((𝐴↑𝑁) + (𝐵↑𝑁)) ≠ (𝐶↑𝑁))
 
15-Sep-2026fltoprmlem2 27976 Lemma 2 for fltoprm 27977: If an integer greater than or equal to 3 is a power of 2, it is a multiple of 4. (Contributed by AV, 15-Sep-2026.)
((𝑁 ∈ (ℤ≥‘3) ∧ 𝐾 ∈ ℕ0 ∧ 𝑁 = (2↑𝐾)) → 4 ∥ 𝑁)
 
15-Sep-2026fltoprmlem1 27975 Lemma 1 for fltoprm 27977: Every positive integer is either a power of 2 or has an odd prime factor. (Contributed by AV, 15-Sep-2026.)
(𝑁 ∈ ℕ → (∃𝑝 ∈ ℙ (2 < 𝑝 ∧ 𝑝 ∥ 𝑁) ∨ ∃𝑛 ∈ ℕ0 𝑁 = (2↑𝑛)))
 
15-Sep-2026flt4ALT 27974 Fermat's last theorem for the exponent four, derived from Fermat's right triangle theorem (which is not proved yet, see fermrtt: after a proof is available, the hypothesis flt4ALT.r can be removed - TODO-AV). (Contributed by AV, 15-Sep-2026.) (Proof modification is discouraged.) (New usage is discouraged.)
(𝜑 → 𝐴 ∈ ℕ)    &   (𝜑 → 𝐵 ∈ ℕ)    &   (𝜑 → 𝐶 ∈ ℕ)    &   (𝜑 → ∀𝑎 ∈ ℕ ∀𝑏 ∈ ℕ ∀𝑐 ∈ ℕ ((𝑎↑4) − (𝑏↑4)) ≠ (𝑐↑2))    ⇒   (𝜑 → ((𝐴↑4) + (𝐵↑4)) ≠ (𝐶↑4))
 
15-Sep-2026flt4 27973 Fermat's last theorem for the exponent four. (Contributed by AV, 15-Sep-2026.)
(𝜑 → 𝐴 ∈ ℕ)    &   (𝜑 → 𝐵 ∈ ℕ)    &   (𝜑 → 𝐶 ∈ ℕ)    ⇒   (𝜑 → ((𝐴↑4) + (𝐵↑4)) ≠ (𝐶↑4))
 
12-Sep-2026isdrng2 20977 A division ring can equivalently be defined as a ring such that the nonzero elements form a group under multiplication (from which it follows that this is the same group as the group of units). (Contributed by Mario Carneiro, 2-Dec-2014.) (Proof shortened by AV, 12-Sep-2026.)
𝐵 = (Base‘𝑅)    &    0 = (0g‘𝑅)    &   𝐺 = ((mulGrp‘𝑅) ↾s (𝐵 ∖ { 0 }))    ⇒   (𝑅 ∈ DivRing ↔ (𝑅 ∈ Ring ∧ 𝐺 ∈ Grp))
 
12-Sep-2026sbcfung 6555 Distribute proper substitution through the function predicate. (Contributed by Alexander van der Vekens, 23-Jul-2017.) Shorten proof and remove dependency on ax-sep 5249 and ax-pr 5391. (Revised by Eric Schmidt, 12-Sep-2026.)
(𝐴 ∈ 𝑉 → ([𝐴 / 𝑥]Fun 𝐹 ↔ Fun ⦋𝐴 / 𝑥⦌𝐹))
 
8-Sep-2026elhf3OLD 9904 Obsolete version of elhf3 9894 as of 17-Sep-2026. (Contributed by Eric Schmidt, 8-Sep-2026.) (Proof modification is discouraged.) (New usage is discouraged.)
(𝐴 ∈ HF ↔ (𝐴 ∈ Fin ∧ 𝐴 ⊆ HF ))
 
8-Sep-2026hffi 9890 Hereditarily finite sets are finite sets. (Contributed by BTernaryTau, 30-Dec-2025.) Restate using the defined HF symbol. (Revised by Eric Schmidt, 8-Sep-2026.)
(𝐴 ∈ HF → 𝐴 ∈ Fin)
 
8-Sep-2026funmpt3 7679 A function in maps-to notation with three arguments is a function. (Contributed by BTernaryTau, 8-Sep-2026.)
Fun (𝑥 ∈ 𝐴, 𝑦 ∈ 𝐵, 𝑧 ∈ 𝐶 ↦ 𝐷)
 
8-Sep-2026mpt3eqdv 7678 An equality deduction for maps-to notation. (Contributed by BTernaryTau, 8-Sep-2026.)
(𝜑 → 𝐴 = 𝐸)    &   (𝜑 → 𝐵 = 𝐹)    &   (𝜑 → 𝐶 = 𝐺)    &   ((𝜑 ∧ (𝑥 ∈ 𝐴 ∧ 𝑦 ∈ 𝐵 ∧ 𝑧 ∈ 𝐶)) → 𝐷 = 𝐻)    ⇒   (𝜑 → (𝑥 ∈ 𝐴, 𝑦 ∈ 𝐵, 𝑧 ∈ 𝐶 ↦ 𝐷) = (𝑥 ∈ 𝐸, 𝑦 ∈ 𝐹, 𝑧 ∈ 𝐺 ↦ 𝐻))
 
8-Sep-2026mosubott 5484 "At most one" remains true inside ordered triple quantification, analogous to mosubopt 5482. (Contributed by BTernaryTau, 8-Sep-2026.)
(∀𝑥∀𝑦∀𝑧∃*𝑤𝜑 → ∃*𝑤∃𝑥∃𝑦∃𝑧(𝐴 = ⟨𝑥, 𝑦, 𝑧⟩ ∧ 𝜑))
 
8-Sep-2026cotsexgw 5463 Substitution of class 𝐴 for ordered triple ⟨𝑥, 𝑦, 𝑧⟩, analogous to copsexgw 5460. (Contributed by BTernaryTau, 8-Sep-2026.)
(𝐴 = ⟨𝑥, 𝑦, 𝑧⟩ → (𝜑 ↔ ∃𝑥∃𝑦∃𝑧(𝐴 = ⟨𝑥, 𝑦, 𝑧⟩ ∧ 𝜑)))
 
8-Sep-2026eqvinot 5457 A variable introduction law for ordered triples, analogous to eqvinop 5456. (Contributed by BTernaryTau, 8-Sep-2026.)
𝐵 ∈ V    &   𝐶 ∈ V    &   𝐷 ∈ V    ⇒   (𝐴 = ⟨𝐵, 𝐶, 𝐷⟩ ↔ ∃𝑥∃𝑦∃𝑧(𝐴 = ⟨𝑥, 𝑦, 𝑧⟩ ∧ ⟨𝑥, 𝑦, 𝑧⟩ = ⟨𝐵, 𝐶, 𝐷⟩))
 
8-Sep-2026ax12ev2c 2217 A commuted form of ax12ev2 2216. (Contributed by BTernaryTau, 8-Sep-2026.)
(𝑥 = 𝑦 → (∃𝑦(𝑥 = 𝑦 ∧ 𝜑) → 𝜑))
 
7-Sep-2026mpt3mpt 7677 Express a three-argument function as a one-argument function, or vice-versa. (Contributed by BTernaryTau, 7-Sep-2026.)
(𝑤 = ⟨𝑥, 𝑦, 𝑧⟩ → 𝐷 = 𝐸)    ⇒   (𝑤 ∈ ((𝐴 × 𝐵) × 𝐶) ↦ 𝐷) = (𝑥 ∈ 𝐴, 𝑦 ∈ 𝐵, 𝑧 ∈ 𝐶 ↦ 𝐸)
 
6-Sep-2026tz7.48lem 8434 A way of showing an ordinal function is one-to-one. (Contributed by NM, 9-Feb-1997.) Extract onelfvnef1 8433. (Proof shortened by Matthew House, 6-Sep-2026.)
𝐹 Fn On    ⇒   ((𝐴 ⊆ On ∧ ∀𝑥 ∈ 𝐴 ∀𝑦 ∈ 𝑥 ¬ (𝐹‘𝑥) = (𝐹‘𝑦)) → Fun ◡(𝐹 ↾ 𝐴))
 
6-Sep-2026onelfvnef1 8433 A sufficient condition for a function on ordinals to be one-to-one. (Contributed by NM, 9-Feb-1997.) Extract from tz7.48lem 8434 and generalize statement. (Revised by Matthew House, 6-Sep-2026.)
((𝐹:𝐴⟶𝐵 ∧ 𝐴 ⊆ On ∧ ∀𝑥 ∈ 𝐴 ∀𝑦 ∈ 𝐴 (𝑦 ∈ 𝑥 → (𝐹‘𝑥) ≠ (𝐹‘𝑦))) → 𝐹:𝐴–1-1→𝐵)
 
4-Sep-20269onn 35753 The ordinal 9 is a natural number. (Contributed by BTernaryTau, 4-Sep-2026.)
9o ∈ ω
 
4-Sep-20268onn 35752 The ordinal 8 is a natural number. (Contributed by BTernaryTau, 4-Sep-2026.)
8o ∈ ω
 
4-Sep-20267onn 35751 The ordinal 7 is a natural number. (Contributed by BTernaryTau, 4-Sep-2026.)
7o ∈ ω
 
4-Sep-20266onn 35750 The ordinal 6 is a natural number. (Contributed by BTernaryTau, 4-Sep-2026.)
6o ∈ ω
 
4-Sep-20265onn 35749 The ordinal 5 is a natural number. (Contributed by BTernaryTau, 4-Sep-2026.)
5o ∈ ω
 
4-Sep-20269on 35748 Ordinal 9 is an ordinal number. (Contributed by BTernaryTau, 4-Sep-2026.)
9o ∈ On
 
4-Sep-20268on 35747 Ordinal 8 is an ordinal number. (Contributed by BTernaryTau, 4-Sep-2026.)
8o ∈ On
 
4-Sep-20267on 35746 Ordinal 7 is an ordinal number. (Contributed by BTernaryTau, 4-Sep-2026.)
7o ∈ On
 
4-Sep-20266on 35745 Ordinal 6 is an ordinal number. (Contributed by BTernaryTau, 4-Sep-2026.)
6o ∈ On
 
4-Sep-20265on 35744 Ordinal 5 is an ordinal number. (Contributed by BTernaryTau, 4-Sep-2026.)
5o ∈ On
 
3-Sep-2026df-l 35853 Define the class of all constructible sets. Definition 15.15 of [TakeutiZaring] p. 158. (Contributed by BTernaryTau, 3-Sep-2026.)
𝐿 = (𝐹𝐿 “ On)
 
3-Sep-2026df-fnl 35852 Define a function whose range contains all and only the constructible sets. Based on Definition 15.13 of [TakeutiZaring] p. 158. (Contributed by BTernaryTau, 3-Sep-2026.)
𝐹𝐿 = recs((𝑥 ∈ V ↦ if((𝐾3‘dom 𝑥) = ∅, ran 𝑥, (ℱ ‘⟨(𝐾3‘dom 𝑥), (𝑥‘(𝐾1‘dom 𝑥)), (𝑥‘(𝐾2‘dom 𝑥))⟩))))
 
2-Sep-2026df-k3 35851 Define a function that takes an ordinal and returns the third argument of the ordered triple ⟨𝑥, 𝑦, 𝑛⟩ such that the ordinal equals (𝐽‘⟨𝑥, 𝑦, 𝑛⟩). Based on the third case of Definition 15.7 of [TakeutiZaring] p. 156. (Contributed by BTernaryTau, 2-Sep-2026.)
𝐾3 = {⟨𝑧, 𝑛⟩ ∣ (𝑛 ∈ 9o ∧ ∃𝑥 ∈ On ∃𝑦 ∈ On 𝑧 = (𝐽‘⟨𝑥, 𝑦, 𝑛⟩))}
 
2-Sep-2026df-k2 35850 Define a function that takes an ordinal and returns the second argument of the ordered triple ⟨𝑥, 𝑦, 𝑛⟩ such that the ordinal equals (𝐽‘⟨𝑥, 𝑦, 𝑛⟩). Based on the second case of Definition 15.7 of [TakeutiZaring] p. 156. (Contributed by BTernaryTau, 2-Sep-2026.)
𝐾2 = {⟨𝑧, 𝑦⟩ ∣ (𝑦 ∈ On ∧ ∃𝑛 ∈ 9o ∃𝑥 ∈ On 𝑧 = (𝐽‘⟨𝑥, 𝑦, 𝑛⟩))}
 
2-Sep-2026df-k1 35849 Define a function that takes an ordinal and returns the first argument of the ordered triple ⟨𝑥, 𝑦, 𝑛⟩ such that the ordinal equals (𝐽‘⟨𝑥, 𝑦, 𝑛⟩). Based on the first case of Definition 15.7 of [TakeutiZaring] p. 156. (Contributed by BTernaryTau, 2-Sep-2026.)
𝐾1 = {⟨𝑧, 𝑥⟩ ∣ (𝑥 ∈ On ∧ ∃𝑛 ∈ 9o ∃𝑦 ∈ On 𝑧 = (𝐽‘⟨𝑥, 𝑦, 𝑛⟩))}
 
2-Sep-2026df-j 35848 Define an order isomorphism from (On × On) × 9o to On. Based on Definition 15.2 of [TakeutiZaring] p. 155. (Contributed by BTernaryTau, 2-Sep-2026.)
𝐽 = (𝑥 ∈ On, 𝑦 ∈ On, 𝑛 ∈ 9o ↦ ((9o ·o (𝐽0‘⟨𝑥, 𝑦⟩)) +o 𝑛))
 
2-Sep-2026df-j0 35847 Define the 𝑅0 order isomorphism from On × On to On. Equivalent to Definition 7.59 of [TakeutiZaring] p. 55. (Contributed by BTernaryTau, 2-Sep-2026.)
𝐽0 = ◡OrdIso(𝑅0, (On × On))
 
2-Sep-2026df-r0 35846 Define a particular set-like well-ordering of On × On using the lexicographical ordering LexOrd. Based on Definition 7.57 of [TakeutiZaring] p. 54. (Contributed by BTernaryTau, 2-Sep-2026.)
𝑅0 = {⟨𝑥, 𝑦⟩ ∣ ((𝑥 ∈ (On × On) ∧ 𝑦 ∈ (On × On)) ∧ (((1st ‘𝑥) ∪ (2nd ‘𝑥)) ∈ ((1st ‘𝑦) ∪ (2nd ‘𝑦)) ∨ (((1st ‘𝑥) ∪ (2nd ‘𝑥)) = ((1st ‘𝑦) ∪ (2nd ‘𝑦)) ∧ 𝑥LexOrd𝑦)))}
 
2-Sep-2026df-lexo 35845 Define the lexicographical ordering of On × On. Based on Definition 7.55 of [TakeutiZaring] p. 54. (Contributed by BTernaryTau, 2-Sep-2026.)
LexOrd = {⟨𝑥, 𝑦⟩ ∣ ((𝑥 ∈ (On × On) ∧ 𝑦 ∈ (On × On)) ∧ ((1st ‘𝑥) ∈ (1st ‘𝑦) ∨ ((1st ‘𝑥) = (1st ‘𝑦) ∧ (2nd ‘𝑥) ∈ (2nd ‘𝑦))))}
 
2-Sep-2026df-gdlopc 35835 Define the combined Gödel operations. This function takes three arguments and uses the first to determine which of the eight Gödel operations df-gdlop1 35827 through df-gdlop8 35834 to apply to the second and third arguments. Based on Definition 14.2 of [TakeutiZaring] p. 144. (Contributed by BTernaryTau, 2-Sep-2026.)
ℱ = (𝑛 ∈ (9o ∖ {∅}), 𝑥 ∈ V, 𝑦 ∈ V ↦ if(𝑛 = 1o, (ℱ1‘⟨𝑥, 𝑦⟩), if(𝑛 = 2o, (ℱ2‘⟨𝑥, 𝑦⟩), if(𝑛 = 3o, (ℱ3‘⟨𝑥, 𝑦⟩), if(𝑛 = 4o, (ℱ4‘⟨𝑥, 𝑦⟩), if(𝑛 = 5o, (ℱ5‘⟨𝑥, 𝑦⟩), if(𝑛 = 6o, (ℱ6‘⟨𝑥, 𝑦⟩), if(𝑛 = 7o, (ℱ7‘⟨𝑥, 𝑦⟩), (ℱ8‘⟨𝑥, 𝑦⟩)))))))))
 
2-Sep-2026df-gdlop8 35834 Define the eighth Gödel operation. This function takes two arguments and returns the intersection of the first argument with the third converse of the second argument (see df-in 3906 and df-cnv3 35826). Based on the eighth case of Definition 14.2 of [TakeutiZaring] p. 144. (Contributed by BTernaryTau, 2-Sep-2026.)
ℱ8 = (𝑥 ∈ V, 𝑦 ∈ V ↦ (𝑥 ∩ (Cnv3‘𝑦)))
 
2-Sep-2026df-gdlop7 35833 Define the seventh Gödel operation. This function takes two arguments and returns the intersection of the first argument with the second converse of the second argument (see df-in 3906 and df-cnv2 35825). Based on the seventh case of Definition 14.2 of [TakeutiZaring] p. 144. (Contributed by BTernaryTau, 2-Sep-2026.)
ℱ7 = (𝑥 ∈ V, 𝑦 ∈ V ↦ (𝑥 ∩ (Cnv2‘𝑦)))
 
2-Sep-2026df-gdlop6 35832 Define the sixth Gödel operation. This function takes two arguments and returns the intersection of the first argument with the converse of the second argument (see df-in 3906 and df-cnv 5659). Based on the sixth case of Definition 14.2 of [TakeutiZaring] p. 144. (Contributed by BTernaryTau, 2-Sep-2026.)
ℱ6 = (𝑥 ∈ V, 𝑦 ∈ V ↦ (𝑥 ∩ ◡𝑦))
 
2-Sep-2026df-gdlop5 35831 Define the fifth Gödel operation. This function takes two arguments and returns the intersection of the first argument with the domain of the second argument (see df-in 3906 and df-dm 5661). Based on the fifth case of Definition 14.2 of [TakeutiZaring] p. 144. (Contributed by BTernaryTau, 2-Sep-2026.)
ℱ5 = (𝑥 ∈ V, 𝑦 ∈ V ↦ (𝑥 ∩ dom 𝑦))
 
2-Sep-2026df-gdlop4 35830 Define the fourth Gödel operation. This function takes two arguments and returns the first argument restricted to the second argument (see df-res 5663). Based on the fourth case of Definition 14.2 of [TakeutiZaring] p. 144. (Contributed by BTernaryTau, 2-Sep-2026.)
ℱ4 = (𝑥 ∈ V, 𝑦 ∈ V ↦ (𝑥 ↾ 𝑦))
 
2-Sep-2026df-gdlop3 35829 Define the third Gödel operation. This function takes two arguments and returns the first argument minus the second argument (see df-dif 3902). Based on the third case of Definition 14.2 of [TakeutiZaring] p. 144. (Contributed by BTernaryTau, 2-Sep-2026.)
ℱ3 = (𝑥 ∈ V, 𝑦 ∈ V ↦ (𝑥 ∖ 𝑦))
 
2-Sep-2026df-gdlop2 35828 Define the second Gödel operation. This function takes two arguments and returns the intersection of the first argument with the membership relation (see df-in 3906 and df-eprel 5551). The second argument is ignored. Based on the second case of Definition 14.2 of [TakeutiZaring] p. 144. (Contributed by BTernaryTau, 2-Sep-2026.)
ℱ2 = (𝑥 ∈ V, 𝑦 ∈ V ↦ (𝑥 ∩ E ))
 
2-Sep-2026df-gdlop1 35827 Define the first Gödel operation. This function takes two arguments and returns the unordered pair containing both (see df-pr 4587). Based on the first case of Definition 14.2 of [TakeutiZaring] p. 144. (Contributed by BTernaryTau, 2-Sep-2026.)
ℱ1 = (𝑥 ∈ V, 𝑦 ∈ V ↦ {𝑥, 𝑦})
 
2-Sep-2026df-cnv3 35826 Define a function that returns the third converse of a set. The third converse of a set takes all ordered triples in the set and swaps the second and third arguments. Based on Definition 14.1(2) of [TakeutiZaring] p. 143. (Contributed by BTernaryTau, 2-Sep-2026.)
Cnv3 = (𝑤 ∈ V ↦ {⟨⟨𝑥, 𝑦⟩, 𝑧⟩ ∣ ⟨⟨𝑥, 𝑧⟩, 𝑦⟩ ∈ 𝑤})
 
2-Sep-2026df-cnv2 35825 Define a function that returns the second converse of a set. The second converse of a set takes all ordered triples in the set and rotates them so the last argument becomes the first argument. Based on Definition 14.1(1) of [TakeutiZaring] p. 143. (Contributed by BTernaryTau, 2-Sep-2026.)
Cnv2 = (𝑤 ∈ V ↦ {⟨⟨𝑥, 𝑦⟩, 𝑧⟩ ∣ ⟨⟨𝑧, 𝑥⟩, 𝑦⟩ ∈ 𝑤})
 
2-Sep-2026df-9o 35743 Define the ordinal number 9. (Contributed by BTernaryTau, 2-Sep-2026.)
9o = suc 8o
 
2-Sep-2026df-8o 35742 Define the ordinal number 8. (Contributed by BTernaryTau, 2-Sep-2026.)
8o = suc 7o
 
2-Sep-2026df-7o 35741 Define the ordinal number 7. (Contributed by BTernaryTau, 2-Sep-2026.)
7o = suc 6o
 
2-Sep-2026df-6o 35740 Define the ordinal number 6. (Contributed by BTernaryTau, 2-Sep-2026.)
6o = suc 5o
 
2-Sep-2026df-5o 35739 Define the ordinal number 5. (Contributed by BTernaryTau, 2-Sep-2026.)
5o = suc 4o
 
31-Aug-2026angmgmbas 29380 The base set of the angle addition magma. (Contributed by Thierry Arnoux, 31-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &    ∼ = (cgrA‘𝐺)    &   𝐽 = (AngMgm‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    ⇒   (𝜑 → (𝐴 / ∼ ) = (Base‘𝐽))
 
31-Aug-2026angmgm 29379 The angle addition magma is a magma. (Contributed by Thierry Arnoux, 31-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    + = (𝑒 ∈ 𝐴, 𝑓 ∈ 𝐴 ↦ if((𝑒‘0) ∈ ((𝑒‘1)𝐿(𝑒‘2)), ⟨“(𝑓‘0)(𝑓‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑓‘2)(𝑓‘1)𝑠”⟩ ∼ 𝑒 ∧ ((𝑓‘1) − 𝑠) = ((𝑒‘1) − (𝑒‘0))))”⟩, ⟨“(𝑒‘0)(𝑒‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑒‘2)(𝑒‘1)𝑠”⟩ ∼ 𝑓 ∧ ((𝑒‘1) − 𝑠) = ((𝑓‘1) − (𝑓‘0)) ∧ (((𝑒‘1)𝐿(𝑒‘2)) ∩ (𝑠𝐼(𝑒‘0))) ≠ ∅))”⟩))    &   𝐽 = (AngMgm‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 2 ≤ (♯‘𝑃))    ⇒   (𝜑 → 𝐽 ∈ Mgm)
 
31-Aug-2026angmgm0g 29378 The identity element of the angle addition magma. (Contributed by Thierry Arnoux, 31-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    + = (𝑒 ∈ 𝐴, 𝑓 ∈ 𝐴 ↦ if((𝑒‘0) ∈ ((𝑒‘1)𝐿(𝑒‘2)), ⟨“(𝑓‘0)(𝑓‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑓‘2)(𝑓‘1)𝑠”⟩ ∼ 𝑒 ∧ ((𝑓‘1) − 𝑠) = ((𝑒‘1) − (𝑒‘0))))”⟩, ⟨“(𝑒‘0)(𝑒‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑒‘2)(𝑒‘1)𝑠”⟩ ∼ 𝑓 ∧ ((𝑒‘1) − 𝑠) = ((𝑓‘1) − (𝑓‘0)) ∧ (((𝑒‘1)𝐿(𝑒‘2)) ∩ (𝑠𝐼(𝑒‘0))) ≠ ∅))”⟩))    &   𝐽 = (AngMgm‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ (𝑃 ∖ {𝑋}))    ⇒   (𝜑 → [⟨“𝑋𝑌𝑋”⟩] ∼ = (0g‘𝐽))
 
31-Aug-2026angmgmlem 29377 Lemma for angmgm 29379. (Contributed by Thierry Arnoux, 31-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    + = (𝑒 ∈ 𝐴, 𝑓 ∈ 𝐴 ↦ if((𝑒‘0) ∈ ((𝑒‘1)𝐿(𝑒‘2)), ⟨“(𝑓‘0)(𝑓‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑓‘2)(𝑓‘1)𝑠”⟩ ∼ 𝑒 ∧ ((𝑓‘1) − 𝑠) = ((𝑒‘1) − (𝑒‘0))))”⟩, ⟨“(𝑒‘0)(𝑒‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑒‘2)(𝑒‘1)𝑠”⟩ ∼ 𝑓 ∧ ((𝑒‘1) − 𝑠) = ((𝑓‘1) − (𝑓‘0)) ∧ (((𝑒‘1)𝐿(𝑒‘2)) ∩ (𝑠𝐼(𝑒‘0))) ≠ ∅))”⟩))    &   𝐽 = (AngMgm‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ (𝑃 ∖ {𝑋}))    ⇒   (𝜑 → (𝐽 ∈ Mgm ∧ [⟨“𝑋𝑌𝑋”⟩] ∼ = (0g‘𝐽)))
 
31-Aug-2026angmgmval 29376 Explicit the value of the angle addition magma for a given geometry 𝐺. (Contributed by Thierry Arnoux, 31-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    + = (𝑒 ∈ 𝐴, 𝑓 ∈ 𝐴 ↦ if((𝑒‘0) ∈ ((𝑒‘1)𝐿(𝑒‘2)), ⟨“(𝑓‘0)(𝑓‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑓‘2)(𝑓‘1)𝑠”⟩ ∼ 𝑒 ∧ ((𝑓‘1) − 𝑠) = ((𝑒‘1) − (𝑒‘0))))”⟩, ⟨“(𝑒‘0)(𝑒‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑒‘2)(𝑒‘1)𝑠”⟩ ∼ 𝑓 ∧ ((𝑒‘1) − 𝑠) = ((𝑓‘1) − (𝑓‘0)) ∧ (((𝑒‘1)𝐿(𝑒‘2)) ∩ (𝑠𝐼(𝑒‘0))) ≠ ∅))”⟩))    &   𝐽 = (AngMgm‘𝐺)    &    ≤ = (≤∠‘𝐺)    ⇒   (𝐺 ∈ 𝑉 → 𝐽 = ({⟨(Base‘ndx), 𝐴⟩, ⟨(+g‘ndx), + ⟩, ⟨(le‘ndx), ≤ ⟩} /s ∼ ))
 
31-Aug-2026angmgmaddrid 29375 The right identity element for the addition of angles. (Contributed by Thierry Arnoux, 31-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &    + = (𝑒 ∈ 𝐴, 𝑓 ∈ 𝐴 ↦ if((𝑒‘0) ∈ ((𝑒‘1)𝐿(𝑒‘2)), ⟨“(𝑓‘0)(𝑓‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑓‘2)(𝑓‘1)𝑠”⟩ ∼ 𝑒 ∧ ((𝑓‘1) − 𝑠) = ((𝑒‘1) − (𝑒‘0))))”⟩, ⟨“(𝑒‘0)(𝑒‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑒‘2)(𝑒‘1)𝑠”⟩ ∼ 𝑓 ∧ ((𝑒‘1) − 𝑠) = ((𝑓‘1) − (𝑓‘0)) ∧ (((𝑒‘1)𝐿(𝑒‘2)) ∩ (𝑠𝐼(𝑒‘0))) ≠ ∅))”⟩))    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ (𝑃 ∖ {𝑋}))    &   (𝜑 → 𝐸 ∈ 𝐴)    ⇒   (𝜑 → (𝐸 + ⟨“𝑋𝑌𝑋”⟩) ∼ 𝐸)
 
31-Aug-2026angmgmaddlid 29374 The left identity element for the addition of angles. (Contributed by Thierry Arnoux, 31-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &    + = (𝑒 ∈ 𝐴, 𝑓 ∈ 𝐴 ↦ if((𝑒‘0) ∈ ((𝑒‘1)𝐿(𝑒‘2)), ⟨“(𝑓‘0)(𝑓‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑓‘2)(𝑓‘1)𝑠”⟩ ∼ 𝑒 ∧ ((𝑓‘1) − 𝑠) = ((𝑒‘1) − (𝑒‘0))))”⟩, ⟨“(𝑒‘0)(𝑒‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑒‘2)(𝑒‘1)𝑠”⟩ ∼ 𝑓 ∧ ((𝑒‘1) − 𝑠) = ((𝑓‘1) − (𝑓‘0)) ∧ (((𝑒‘1)𝐿(𝑒‘2)) ∩ (𝑠𝐼(𝑒‘0))) ≠ ∅))”⟩))    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ (𝑃 ∖ {𝑋}))    &   (𝜑 → 𝐸 ∈ 𝐴)    ⇒   (𝜑 → (⟨“𝑋𝑌𝑋”⟩ + 𝐸) ∼ 𝐸)
 
31-Aug-2026angmgmaddcl 29373 Closure of the addition of angles. (Contributed by Thierry Arnoux, 31-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &    + = (𝑒 ∈ 𝐴, 𝑓 ∈ 𝐴 ↦ if((𝑒‘0) ∈ ((𝑒‘1)𝐿(𝑒‘2)), ⟨“(𝑓‘0)(𝑓‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑓‘2)(𝑓‘1)𝑠”⟩ ∼ 𝑒 ∧ ((𝑓‘1) − 𝑠) = ((𝑒‘1) − (𝑒‘0))))”⟩, ⟨“(𝑒‘0)(𝑒‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑒‘2)(𝑒‘1)𝑠”⟩ ∼ 𝑓 ∧ ((𝑒‘1) − 𝑠) = ((𝑓‘1) − (𝑓‘0)) ∧ (((𝑒‘1)𝐿(𝑒‘2)) ∩ (𝑠𝐼(𝑒‘0))) ≠ ∅))”⟩))    &   (𝜑 → 𝐸 ∈ 𝐴)    &   (𝜑 → 𝐹 ∈ 𝐴)    ⇒   (𝜑 → (𝐸 + 𝐹) ∈ 𝐴)
 
31-Aug-2026cgrabasimass 29360 The angle congruence relation is hereditary. (Contributed by Thierry Arnoux, 31-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &    ∼ = (cgrA‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    ⇒   (𝜑 → ( ∼ “ 𝐴) ⊆ 𝐴)
 
31-Aug-2026cgraer 29359 The angle congruence relation is an equivalence relation. (Contributed by Thierry Arnoux, 31-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &    ∼ = (cgrA‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    ⇒   (𝜑 → ( ∼ ∩ (𝐴 × 𝐴)) Er 𝐴)
 
31-Aug-2026qusmnd 18955 Prove that a quotient structure is a monoid. (Contributed by Thierry Arnoux, 31-Aug-2026.)
(𝜑 → 𝑈 = (𝑅 /s ∼ ))    &   (𝜑 → 𝑉 = (Base‘𝑅))    &    + = (+g‘𝑅)    &   (𝜑 → ∼ Er 𝑉)    &   (𝜑 → 𝑅 ∈ 𝑋)    &   (𝜑 → ((𝑎 ∼ 𝑝 ∧ 𝑏 ∼ 𝑞) → (𝑎 + 𝑏) ∼ (𝑝 + 𝑞)))    &   ((𝜑 ∧ 𝑥 ∈ 𝑉 ∧ 𝑦 ∈ 𝑉) → (𝑥 + 𝑦) ∈ 𝑉)    &   ((𝜑 ∧ (𝑥 ∈ 𝑉 ∧ 𝑦 ∈ 𝑉 ∧ 𝑧 ∈ 𝑉)) → ((𝑥 + 𝑦) + 𝑧) ∼ (𝑥 + (𝑦 + 𝑧)))    &   (𝜑 → 0 ∈ 𝑉)    &   ((𝜑 ∧ 𝑥 ∈ 𝑉) → ( 0 + 𝑥) ∼ 𝑥)    &   ((𝜑 ∧ 𝑥 ∈ 𝑉) → (𝑥 + 0 ) ∼ 𝑥)    ⇒   (𝜑 → (𝑈 ∈ Mnd ∧ [ 0 ] ∼ = (0g‘𝑈)))
 
31-Aug-2026qusmgm 18844 Prove that a quotient structure is a unital magma. (Contributed by Thierry Arnoux, 31-Aug-2026.)
(𝜑 → 𝑈 = (𝑅 /s ∼ ))    &   (𝜑 → 𝑉 = (Base‘𝑅))    &    + = (+g‘𝑅)    &   (𝜑 → ∼ Er 𝑉)    &   (𝜑 → 𝑅 ∈ 𝑋)    &   (𝜑 → ((𝑎 ∼ 𝑝 ∧ 𝑏 ∼ 𝑞) → (𝑎 + 𝑏) ∼ (𝑝 + 𝑞)))    &   ((𝜑 ∧ 𝑥 ∈ 𝑉 ∧ 𝑦 ∈ 𝑉) → (𝑥 + 𝑦) ∈ 𝑉)    &   (𝜑 → 0 ∈ 𝑉)    &   ((𝜑 ∧ 𝑥 ∈ 𝑉) → ( 0 + 𝑥) ∼ 𝑥)    &   ((𝜑 ∧ 𝑥 ∈ 𝑉) → (𝑥 + 0 ) ∼ 𝑥)    ⇒   (𝜑 → (𝑈 ∈ Mgm ∧ [ 0 ] ∼ = (0g‘𝑈)))
 
31-Aug-2026imasmgm2 18843 The image structure of a unital magma is a unital magma. (Contributed by Thierry Arnoux, 31-Aug-2026.)
(𝜑 → 𝑈 = (𝐹 “s 𝑅))    &   (𝜑 → 𝑉 = (Base‘𝑅))    &    + = (+g‘𝑅)    &   (𝜑 → 𝐹:𝑉–onto→𝐵)    &   ((𝜑 ∧ (𝑎 ∈ 𝑉 ∧ 𝑏 ∈ 𝑉) ∧ (𝑝 ∈ 𝑉 ∧ 𝑞 ∈ 𝑉)) → (((𝐹‘𝑎) = (𝐹‘𝑝) ∧ (𝐹‘𝑏) = (𝐹‘𝑞)) → (𝐹‘(𝑎 + 𝑏)) = (𝐹‘(𝑝 + 𝑞))))    &   (𝜑 → 𝑅 ∈ 𝑊)    &   ((𝜑 ∧ 𝑥 ∈ 𝑉 ∧ 𝑦 ∈ 𝑉) → (𝑥 + 𝑦) ∈ 𝑉)    &   (𝜑 → 0 ∈ 𝑉)    &   ((𝜑 ∧ 𝑥 ∈ 𝑉) → (𝐹‘( 0 + 𝑥)) = (𝐹‘𝑥))    &   ((𝜑 ∧ 𝑥 ∈ 𝑉) → (𝐹‘(𝑥 + 0 )) = (𝐹‘𝑥))    ⇒   (𝜑 → (𝑈 ∈ Mgm ∧ (𝐹‘ 0 ) = (0g‘𝑈)))
 
30-Aug-2026smflimlem6 47730 Lemma for the proof that the limit of sigma-measurable functions is sigma-measurable, Proposition 121F (a) of [Fremlin1] p. 38 . This lemma proves that the preimages of right-closed, unbounded-below intervals are in the subspace sigma-algebra induced by 𝐷. The proof uses fnrndomnum 10598 rather than fnrndomg 10599, and so does not require ax-ac 10518. (Contributed by Glauco Siliprandi, 26-Jun-2021.) (Revised by Vincent Gonzalez, 30-Aug-2026.)
(𝜑 → 𝑀 ∈ ℤ)    &   𝑍 = (ℤ≥‘𝑀)    &   (𝜑 → 𝑆 ∈ SAlg)    &   (𝜑 → 𝐹:𝑍⟶(SMblFn‘𝑆))    &   𝐷 = {𝑥 ∈ ∪ 𝑛 ∈ 𝑍 ∩ 𝑚 ∈ (ℤ≥‘𝑛)dom (𝐹‘𝑚) ∣ (𝑚 ∈ 𝑍 ↦ ((𝐹‘𝑚)‘𝑥)) ∈ dom ⇝ }    &   𝐺 = (𝑥 ∈ 𝐷 ↦ ( ⇝ ‘(𝑚 ∈ 𝑍 ↦ ((𝐹‘𝑚)‘𝑥))))    &   (𝜑 → 𝐴 ∈ ℝ)    &   𝑃 = (𝑚 ∈ 𝑍, 𝑘 ∈ ℕ ↦ {𝑠 ∈ 𝑆 ∣ {𝑥 ∈ dom (𝐹‘𝑚) ∣ ((𝐹‘𝑚)‘𝑥) < (𝐴 + (1 / 𝑘))} = (𝑠 ∩ dom (𝐹‘𝑚))})    ⇒   (𝜑 → {𝑥 ∈ 𝐷 ∣ (𝐺‘𝑥) ≤ 𝐴} ∈ (𝑆 ↾t 𝐷))
 
30-Aug-2026subsaliuncl 47312 A subspace sigma-algebra is closed under countable union. This is Lemma 121A (iii) of [Fremlin1] p. 35. The proof uses fnrndomnum 10598 rather than fnrndomg 10599, and so does not require ax-ac 10518. (Contributed by Glauco Siliprandi, 26-Jun-2021.) (Revised by Vincent Gonzalez, 30-Aug-2026.)
(𝜑 → 𝑆 ∈ SAlg)    &   (𝜑 → 𝐷 ∈ 𝑉)    &   𝑇 = (𝑆 ↾t 𝐷)    &   (𝜑 → 𝐹:ℕ⟶𝑇)    ⇒   (𝜑 → ∪ 𝑛 ∈ ℕ (𝐹‘𝑛) ∈ 𝑇)
 
30-Aug-2026preimaaa 26628 An element of the preimage of the algebraic numbers by a nonconstant polynomial is an algebraic number. (Contributed by SN, 30-Aug-2026.)
(𝜑 → 𝐹 ∈ (Poly‘ℚ))    &   (𝜑 → (deg‘𝐹) ≠ 0)    &   (𝜑 → 𝐴 ∈ ℂ)    &   (𝜑 → (𝐹‘𝐴) ∈ 𝔸)    ⇒   (𝜑 → 𝐴 ∈ 𝔸)
 
30-Aug-2026plyconz 26613 The composition of a nonzero and a nonconstant polynomial is a nonzero polynomial. (Contributed by SN, 30-Aug-2026.)
(𝜑 → 𝐹 ∈ (Poly‘𝑆))    &   (𝜑 → 𝐺 ∈ (Poly‘𝑆))    &   (𝜑 → 𝐹 ≠ 0𝑝)    &   (𝜑 → (deg‘𝐺) ≠ 0)    ⇒   (𝜑 → (𝐹 ∘ 𝐺) ≠ 0𝑝)
 
30-Aug-2026rnplynfin 26612 The range of a nonconstant polynomial is not a finite set. (Contributed by SN, 30-Aug-2026.)
(𝜑 → 𝐹 ∈ (Poly‘𝑆))    &   (𝜑 → (deg‘𝐹) ≠ 0)    ⇒   (𝜑 → ¬ ran 𝐹 ∈ Fin)
 
30-Aug-2026idpfv 26508 Value of the identity polynomial. (Contributed by SN, 30-Aug-2026.)
(𝐴 ∈ ℂ → (Xp‘𝐴) = 𝐴)
 
30-Aug-20261q 13073 The number 1 is rational. (Contributed by SN, 30-Aug-2026.)
1 ∈ ℚ
 
30-Aug-2026elmaprd 8854 Deduction associated with elmapd 8844. Reverse direction of elmapdd 8845. (Contributed by Thierry Arnoux, 13-Oct-2025.) Removed redundant hypotheses. (Revised by SN, 30-Aug-2026.)
(𝜑 → 𝐹 ∈ (𝐵 ↑m 𝐴))    ⇒   (𝜑 → 𝐹:𝐴⟶𝐵)
 
28-Aug-2026dvcot 50802 Derivative of the cotangent function. (Contributed by Jon Pennant, 28-Aug-2026.)
(ℂ D cot) = (𝑥 ∈ dom cot ↦ -((csc‘𝑥)↑2))
 
28-Aug-2026dvcsc 50801 Derivative of the cosecant function. (Contributed by Jon Pennant, 28-Aug-2026.)
(ℂ D csc) = (𝑥 ∈ dom csc ↦ (-(csc‘𝑥) · (cot‘𝑥)))
 
28-Aug-2026dvsec 50800 Derivative of the secant function. (Contributed by Jon Pennant, 28-Aug-2026.)
(ℂ D sec) = (𝑥 ∈ dom sec ↦ ((sec‘𝑥) · (tan‘𝑥)))
 
27-Aug-2026veroquaddetzerod 50930 The Veronese matrix of six points satisfying a common nonzero homogeneous quadratic equation has determinant zero. (Contributed by Jiamin Zhao, 27-Aug-2026.)
𝑉 = (𝑖 ∈ (1...6), 𝑗 ∈ (1...6) ↦ ((veronese‘(𝐴‘𝑖))‘𝑗))    &   (𝜑 → 𝐴:(1...6)⟶(ℝ ↑m (1...3)))    &   (𝜑 → 𝐾:(1...6)⟶ℝ)    &   ((𝜑 ∧ 𝑖 ∈ (1...6)) → (((((𝐾‘1) · (((𝐴‘𝑖)‘1)↑2)) + ((𝐾‘2) · (((𝐴‘𝑖)‘2)↑2))) + ((𝐾‘3) · (((𝐴‘𝑖)‘3)↑2))) + ((((𝐾‘4) · (((𝐴‘𝑖)‘1) · ((𝐴‘𝑖)‘2))) + ((𝐾‘5) · (((𝐴‘𝑖)‘2) · ((𝐴‘𝑖)‘3)))) + ((𝐾‘6) · (((𝐴‘𝑖)‘3) · ((𝐴‘𝑖)‘1))))) = 0)    &   (𝜑 → 𝐾 ≠ ((1...6) × {0}))    ⇒   (𝜑 → (((1...6) maDet ℝfld)‘𝑉) = 0)
 
27-Aug-2026veroquadnolindfd 50929 A nonzero homogeneous quadratic equation satisfied by all six points gives a linear dependence among the columns of the Veronese matrix. (Contributed by Jiamin Zhao, 27-Aug-2026.)
𝑉 = (𝑖 ∈ (1...6), 𝑗 ∈ (1...6) ↦ ((veronese‘(𝐴‘𝑖))‘𝑗))    &   (𝜑 → 𝐴:(1...6)⟶(ℝ ↑m (1...3)))    &   (𝜑 → 𝐾:(1...6)⟶ℝ)    &   ((𝜑 ∧ 𝑖 ∈ (1...6)) → (((((𝐾‘1) · (((𝐴‘𝑖)‘1)↑2)) + ((𝐾‘2) · (((𝐴‘𝑖)‘2)↑2))) + ((𝐾‘3) · (((𝐴‘𝑖)‘3)↑2))) + ((((𝐾‘4) · (((𝐴‘𝑖)‘1) · ((𝐴‘𝑖)‘2))) + ((𝐾‘5) · (((𝐴‘𝑖)‘2) · ((𝐴‘𝑖)‘3)))) + ((𝐾‘6) · (((𝐴‘𝑖)‘3) · ((𝐴‘𝑖)‘1))))) = 0)    &   (𝜑 → 𝐾 ≠ ((1...6) × {0}))    ⇒   (𝜑 → ¬ curry tpos 𝑉 LIndF (ℝfld freeLMod (1...6)))
 
27-Aug-2026nellindf 50914 A nonzero coefficient vector whose weighted combination of 𝐹 sums to the zero vector implies that 𝐹 is not linearly independent. (Contributed by Jiamin Zhao, 27-Aug-2026.)
𝐵 = (Base‘𝑊)    &   𝑅 = (Scalar‘𝑊)    &    · = ( ·𝑠 ‘𝑊)    &    0 = (0g‘𝑊)    &   𝑌 = (0g‘𝑅)    &   𝐿 = (Base‘(𝑅 freeLMod 𝐼))    ⇒   (((𝑊 ∈ LMod ∧ 𝐼 ∈ V ∧ 𝐹:𝐼⟶𝐵) ∧ (𝐾 ∈ 𝐿 ∧ 𝐾 ≠ (𝐼 × {𝑌}) ∧ (𝑊 Σg (𝐾 ∘f · 𝐹)) = 0 )) → ¬ 𝐹 LIndF 𝑊)
 
26-Aug-2026dffr7 36690 Alternate quantifier-free definition of a well-founded relation. (Contributed by Scott Fenton, 26-Aug-2026.)
(𝑅 Fr 𝐴 ↔ (𝒫 𝐴 ∖ {∅}) ⊆ Fix ( E ∘ (V ∖ (𝑅 ∘ ◡ E ))))
 
26-Aug-2026dffr5 36488 A quantifier-free definition of a well-founded relation. (Contributed by Scott Fenton, 11-Apr-2011.) (Proof shortened by Scott Fenton, 26-Aug-2026.)
(𝑅 Fr 𝐴 ↔ (𝒫 𝐴 ∖ {∅}) ⊆ ran ( E ∖ ( E ∘ ◡𝑅)))
 
26-Aug-2026drngprops 20976 Properties of a division ring. (Contributed by NM, 4-Apr-2009.) (Revised by AV, 26-Aug-2026.)
𝐵 = (Base‘𝑅)    &    0 = (0g‘𝑅)    &   𝐺 = ((mulGrp‘𝑅) ↾s (𝐵 ∖ { 0 }))    ⇒   (𝑅 ∈ DivRing → (𝑅 ∈ Ring ∧ 𝐺 ∈ Grp))
 
26-Aug-2026cnvxp 6146 The converse of a Cartesian product. Exercise 11 of [Suppes] p. 67. (Contributed by NM, 14-Aug-1999.) (Proof shortened by Andrew Salmon, 27-Aug-2011.) Avoid ax-11 2194. (Revised by SN, 26-Aug-2026.)
◡(𝐴 × 𝐵) = (𝐵 × 𝐴)
 
25-Aug-2026fimact 10596 The image by a function of a countable set is countable. The proof uses imadomnum 10595 rather than imadomg 10594, and so does not require ax-ac 10518. (Contributed by Thierry Arnoux, 27-Mar-2018.) (Revised by Vincent Gonzalez, 25-Aug-2026.)
((𝐴 ≼ ω ∧ Fun 𝐹) → (𝐹 “ 𝐴) ≼ ω)
 
25-Aug-2026imadomnum 10595 A version of imadomg 10594 that does not require the axiom of choice ax-ac 10518. (Contributed by Vincent Gonzalez, 25-Aug-2026.)
(𝐴 ∈ dom card → (Fun 𝐹 → (𝐹 “ 𝐴) ≼ 𝐴))
 
24-Aug-20264p5e9 43292 4 + 5 = 9. (Contributed by SN, 24-Aug-2026.)
(4 + 5) = 9
 
24-Aug-20263p6e9 43291 3 + 6 = 9. (Contributed by SN, 24-Aug-2026.)
(3 + 6) = 9
 
24-Aug-20263p5e8 43290 3 + 5 = 8. (Contributed by SN, 24-Aug-2026.)
(3 + 5) = 8
 
24-Aug-20263p4e7 43289 3 + 4 = 7. (Contributed by SN, 24-Aug-2026.)
(3 + 4) = 7
 
24-Aug-20262p7e9 43288 2 + 7 = 9. (Contributed by SN, 24-Aug-2026.)
(2 + 7) = 9
 
24-Aug-20262p6e8 43287 2 + 6 = 8. (Contributed by SN, 24-Aug-2026.)
(2 + 6) = 8
 
24-Aug-20262p5e7 43286 2 + 5 = 7. (Contributed by SN, 24-Aug-2026.)
(2 + 5) = 7
 
24-Aug-20262p4e6 43285 2 + 4 = 6. (Contributed by SN, 24-Aug-2026.)
(2 + 4) = 6
 
24-Aug-20262p3e5 43284 2 + 3 = 5. (Contributed by SN, 24-Aug-2026.)
(2 + 3) = 5
 
24-Aug-20261p8e9 43283 1 + 8 = 9. (Contributed by SN, 24-Aug-2026.)
(1 + 8) = 9
 
24-Aug-20261p7e8 43282 1 + 7 = 8. (Contributed by SN, 24-Aug-2026.)
(1 + 7) = 8
 
24-Aug-20261p6e7 43281 1 + 6 = 7. (Contributed by SN, 24-Aug-2026.)
(1 + 6) = 7
 
24-Aug-20261p5e6 43280 1 + 5 = 6. (Contributed by SN, 24-Aug-2026.)
(1 + 5) = 6
 
24-Aug-20261p4e5 43279 1 + 4 = 5. (Contributed by SN, 24-Aug-2026.)
(1 + 4) = 5
 
24-Aug-20264p4e8ALT 43277 A shorter proof of 4p4e8 12478 if 6p2e8 12482 was moved up. The most clean way to do this would be to start with 7p2e9 12484, then go 6p2e8 12482, 6p3e9 12483, etc., which is still inelegant. The idea here is that using 4 = 2 + 2 and 2cn 12399 is shorter than using 4 = 3 + 1, 3cn 12405, and ax-1cn 11239. This also works with 5p4e9 12481. (Contributed by SN, 24-Aug-2026.) (Proof modification is discouraged.) (New usage is discouraged.)
(4 + 4) = 8
 
24-Aug-2026rsp2idlid 33913 The ideal span of a two-sided ideal is the ideal itself. (Contributed by Jeff Madsen, 10-Jun-2010.) (Revised by AV, 24-Aug-2026.)
𝐾 = (RSpan‘𝑅)    &   𝑈 = (2Ideal‘𝑅)    ⇒   ((𝑅 ∈ Ring ∧ 𝐼 ∈ 𝑈) → (𝐾‘𝐼) = 𝐼)
 
24-Aug-2026ffsrn 33302 The range of a finitely supported function is finite. The proof uses fnrndomnum 10598 rather than fnrndomg 10599, and so does not require ax-ac 10518. (Contributed by Thierry Arnoux, 27-Aug-2017.) (Revised by Vincent Gonzalez, 24-Aug-2026.)
(𝜑 → 𝑍 ∈ 𝑊)    &   (𝜑 → 𝐹 ∈ 𝑉)    &   (𝜑 → Fun 𝐹)    &   (𝜑 → (𝐹 supp 𝑍) ∈ Fin)    ⇒   (𝜑 → ran 𝐹 ∈ Fin)
 
24-Aug-2026ker2idl 21553 The kernel of a ring homomorphism is a two-sided ideal. (Contributed by Jeff Madsen, 3-Jan-2011.) (Revised by AV, 24-Aug-2026.)
𝐼 = (2Ideal‘𝑅)    &    0 = (0g‘𝑆)    ⇒   (𝐹 ∈ (𝑅 RingHom 𝑆) → (◡𝐹 “ { 0 }) ∈ 𝐼)
 
24-Aug-20262idl1el 21529 A two-sided ideal contains 1 iff it is the unit ideal. (Contributed by Jeff Madsen, 10-Jun-2010.) (Revised by AV, 24-Aug-2026.)
𝑈 = (2Ideal‘𝑅)    &   𝐵 = (Base‘𝑅)    &    1 = (1r‘𝑅)    ⇒   ((𝑅 ∈ Ring ∧ 𝐼 ∈ 𝑈) → ( 1 ∈ 𝐼 ↔ 𝐼 = 𝐵))
 
24-Aug-2026dfring3 20498 The predicate "is a (unital) ring" based on a ring being abelian and with the definition of a monoid expanded. (Contributed by Jeff Hankins, 21-Nov-2006.) (Revised by AV, 24-Aug-2026.)
𝐵 = (Base‘𝑅)    &    · = (.r‘𝑅)    &   𝐺 = (mulGrp‘𝑅)    &    + = (+g‘𝑅)    ⇒   (𝑅 ∈ Ring ↔ ((𝑅 ∈ Abel ∧ 𝐺 ∈ Mgm) ∧ ∀𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐵 ∀𝑧 ∈ 𝐵 (((𝑥 · 𝑦) · 𝑧) = (𝑥 · (𝑦 · 𝑧)) ∧ (𝑥 · (𝑦 + 𝑧)) = ((𝑥 · 𝑦) + (𝑥 · 𝑧)) ∧ ((𝑥 + 𝑦) · 𝑧) = ((𝑥 · 𝑧) + (𝑦 · 𝑧))) ∧ ∃𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐵 ((𝑥 · 𝑦) = 𝑦 ∧ (𝑦 · 𝑥) = 𝑦)))
 
24-Aug-2026idvalriota 18821 The unique value of the group identity element. (Contributed by FL, 12-Dec-2009.) (Revised by AV, 24-Aug-2026.)
𝐵 = (Base‘𝐺)    &    + = (+g‘𝐺)    &    0 = (0g‘𝐺)    ⇒    0 = (℩𝑒 ∈ 𝐵 ∀𝑥 ∈ 𝐵 ((𝑒 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑒) = 𝑥))
 
24-Aug-2026fnct 10601 If the domain of a function is countable, the function is countable. The proof uses fnrndomnum 10598 rather than fnrndomg 10599, and so does not require ax-ac 10518. (Contributed by Thierry Arnoux, 29-Dec-2016.) (Revised by Vincent Gonzalez, 24-Aug-2026.)
((𝐹 Fn 𝐴 ∧ 𝐴 ≼ ω) → 𝐹 ≼ ω)
 
24-Aug-2026dmct 10583 The domain of a countable set is countable. The proof uses fodomnum 10117 rather than fodomg 10581, and so does not require ax-ac 10518. (Contributed by Thierry Arnoux, 29-Dec-2016.) (Revised by Vincent Gonzalez, 24-Aug-2026.)
(𝐴 ≼ ω → dom 𝐴 ≼ ω)
 
23-Aug-2026angmgmaddcpbl 29372 Addition of angles is compatible with angle congruence. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &    + = (𝑒 ∈ 𝐴, 𝑓 ∈ 𝐴 ↦ if((𝑒‘0) ∈ ((𝑒‘1)𝐿(𝑒‘2)), ⟨“(𝑓‘0)(𝑓‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑓‘2)(𝑓‘1)𝑠”⟩ ∼ 𝑒 ∧ ((𝑓‘1) − 𝑠) = ((𝑒‘1) − (𝑒‘0))))”⟩, ⟨“(𝑒‘0)(𝑒‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑒‘2)(𝑒‘1)𝑠”⟩ ∼ 𝑓 ∧ ((𝑒‘1) − 𝑠) = ((𝑓‘1) − (𝑓‘0)) ∧ (((𝑒‘1)𝐿(𝑒‘2)) ∩ (𝑠𝐼(𝑒‘0))) ≠ ∅))”⟩))    &   (𝜑 → 𝐶 ∈ 𝐴)    &   (𝜑 → 𝐷 ∈ 𝐴)    &   (𝜑 → 𝐸 ∈ 𝐴)    &   (𝜑 → 𝐹 ∈ 𝐴)    &   (𝜑 → 𝐸 ∼ 𝐶)    &   (𝜑 → 𝐹 ∼ 𝐷)    ⇒   (𝜑 → (𝐸 + 𝐹) ∼ (𝐶 + 𝐷))
 
23-Aug-2026angmgmaddov2 29371 Value of the addition operation in the angle addition magma, in case the first angle is zero or flat. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑈 ≠ 𝑉)    &   (𝜑 → 𝑉 ≠ 𝑊)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → 𝑌 ≠ 𝑍)    &    + = (𝑒 ∈ 𝐴, 𝑓 ∈ 𝐴 ↦ if((𝑒‘0) ∈ ((𝑒‘1)𝐿(𝑒‘2)), ⟨“(𝑓‘0)(𝑓‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑓‘2)(𝑓‘1)𝑠”⟩ ∼ 𝑒 ∧ ((𝑓‘1) − 𝑠) = ((𝑒‘1) − (𝑒‘0))))”⟩, ⟨“(𝑒‘0)(𝑒‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑒‘2)(𝑒‘1)𝑠”⟩ ∼ 𝑓 ∧ ((𝑒‘1) − 𝑠) = ((𝑓‘1) − (𝑓‘0)) ∧ (((𝑒‘1)𝐿(𝑒‘2)) ∩ (𝑠𝐼(𝑒‘0))) ≠ ∅))”⟩))    &   (𝜑 → 𝑋 ∈ (𝑌𝐿𝑍))    &   (𝜑 → 𝑆 ∈ 𝑃)    &   (𝜑 → ⟨“𝑊𝑉𝑆”⟩ ∼ ⟨“𝑋𝑌𝑍”⟩)    &   (𝜑 → (𝑉 − 𝑆) = (𝑌 − 𝑋))    ⇒   (𝜑 → (⟨“𝑋𝑌𝑍”⟩ + ⟨“𝑈𝑉𝑊”⟩) = ⟨“𝑈𝑉𝑆”⟩)
 
23-Aug-2026angmgmaddov1 29370 Value of the addition operation in the angle addition magma, in case the first angle is neither zero nor flat. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑈 ≠ 𝑉)    &   (𝜑 → 𝑉 ≠ 𝑊)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → 𝑌 ≠ 𝑍)    &    + = (𝑒 ∈ 𝐴, 𝑓 ∈ 𝐴 ↦ if((𝑒‘0) ∈ ((𝑒‘1)𝐿(𝑒‘2)), ⟨“(𝑓‘0)(𝑓‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑓‘2)(𝑓‘1)𝑠”⟩ ∼ 𝑒 ∧ ((𝑓‘1) − 𝑠) = ((𝑒‘1) − (𝑒‘0))))”⟩, ⟨“(𝑒‘0)(𝑒‘1)(℩𝑠 ∈ 𝑃 (⟨“(𝑒‘2)(𝑒‘1)𝑠”⟩ ∼ 𝑓 ∧ ((𝑒‘1) − 𝑠) = ((𝑓‘1) − (𝑓‘0)) ∧ (((𝑒‘1)𝐿(𝑒‘2)) ∩ (𝑠𝐼(𝑒‘0))) ≠ ∅))”⟩))    &   (𝜑 → ¬ 𝑋 ∈ (𝑌𝐿𝑍))    &   (𝜑 → 𝑆 ∈ 𝑃)    &   (𝜑 → ⟨“𝑍𝑌𝑆”⟩ ∼ ⟨“𝑈𝑉𝑊”⟩)    &   (𝜑 → (𝑌 − 𝑆) = (𝑉 − 𝑈))    &   (𝜑 → ((𝑌𝐿𝑍) ∩ (𝑆𝐼𝑋)) ≠ ∅)    ⇒   (𝜑 → (⟨“𝑋𝑌𝑍”⟩ + ⟨“𝑈𝑉𝑊”⟩) = ⟨“𝑋𝑌𝑆”⟩)
 
23-Aug-2026angmgmaddov2lem 29369 Lemma for angmgmaddov2 29371. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑈 ≠ 𝑉)    &   (𝜑 → 𝑉 ≠ 𝑊)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → 𝑌 ≠ 𝑍)    &   (𝜑 → 𝑋 ∈ (𝑌𝐿𝑍))    ⇒   (𝜑 → ∃!𝑠 ∈ 𝑃 (⟨“𝑊𝑉𝑠”⟩ ∼ ⟨“𝑋𝑌𝑍”⟩ ∧ (𝑉 − 𝑠) = (𝑌 − 𝑋)))
 
23-Aug-2026angmgmaddov1lem 29368 Lemma for angmgmaddov1 29370. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑈 ≠ 𝑉)    &   (𝜑 → 𝑉 ≠ 𝑊)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → 𝑌 ≠ 𝑍)    &   (𝜑 → ¬ 𝑋 ∈ (𝑌𝐿𝑍))    ⇒   (𝜑 → ∃!𝑠 ∈ 𝑃 (⟨“𝑍𝑌𝑠”⟩ ∼ ⟨“𝑈𝑉𝑊”⟩ ∧ (𝑌 − 𝑠) = (𝑉 − 𝑈) ∧ ((𝑌𝐿𝑍) ∩ (𝑠𝐼𝑋)) ≠ ∅))
 
23-Aug-2026angmgmaddeu7 29367 There exists a unique point 𝑠 satisfying the conditions of angle addition. Case where both angles are straight angles. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑈 ≠ 𝑉)    &   (𝜑 → 𝑉 ≠ 𝑊)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → 𝑌 ≠ 𝑍)    &   (𝜑 → 𝑌 ∈ (𝑋𝐼𝑍))    &   (𝜑 → 𝑉 ∈ (𝑈𝐼𝑊))    ⇒   (𝜑 → ∃!𝑠 ∈ 𝑃 (⟨“𝑍𝑌𝑠”⟩ ∼ ⟨“𝑈𝑉𝑊”⟩ ∧ (𝑌 − 𝑠) = (𝑉 − 𝑈)))
 
23-Aug-2026angmgmaddeu6 29366 There exists a unique point 𝑠 satisfying the conditions of angle addition. Case where the first angle is a zero angle, and the second angle is a straight angle. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑈 ≠ 𝑉)    &   (𝜑 → 𝑉 ≠ 𝑊)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → 𝑌 ≠ 𝑍)    &   (𝜑 → 𝑌 ∈ (𝑋𝐼𝑍))    &   (𝜑 → 𝑈((hlG‘𝐺)‘𝑉)𝑊)    ⇒   (𝜑 → ∃!𝑠 ∈ 𝑃 (⟨“𝑍𝑌𝑠”⟩ ∼ ⟨“𝑈𝑉𝑊”⟩ ∧ (𝑌 − 𝑠) = (𝑉 − 𝑈)))
 
23-Aug-2026angmgmaddeu5 29365 There exists a unique point 𝑠 satisfying the conditions of angle addition. Case where one angle is a zero angle, and the other angle is a straight angle. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑈 ≠ 𝑉)    &   (𝜑 → 𝑉 ≠ 𝑊)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → 𝑌 ≠ 𝑍)    &   (𝜑 → 𝑋((hlG‘𝐺)‘𝑌)𝑍)    &   (𝜑 → 𝑉 ∈ (𝑈𝐼𝑊))    ⇒   (𝜑 → ∃!𝑠 ∈ 𝑃 (⟨“𝑍𝑌𝑠”⟩ ∼ ⟨“𝑈𝑉𝑊”⟩ ∧ (𝑌 − 𝑠) = (𝑉 − 𝑈)))
 
23-Aug-2026angmgmaddeu4 29364 There exists a unique point 𝑠 satisfying the conditions of angle addition. Case where both angles are zero angles. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑈 ≠ 𝑉)    &   (𝜑 → 𝑉 ≠ 𝑊)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → 𝑌 ≠ 𝑍)    &   (𝜑 → 𝑋((hlG‘𝐺)‘𝑌)𝑍)    &   (𝜑 → 𝑈((hlG‘𝐺)‘𝑉)𝑊)    ⇒   (𝜑 → ∃!𝑠 ∈ 𝑃 (⟨“𝑍𝑌𝑠”⟩ ∼ ⟨“𝑈𝑉𝑊”⟩ ∧ (𝑌 − 𝑠) = (𝑉 − 𝑈)))
 
23-Aug-2026angmgmaddeu3 29363 Existence of a unique point for building angle addition. Case where the second angle is a flat angle. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑈 ≠ 𝑉)    &   (𝜑 → 𝑉 ≠ 𝑊)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → 𝑌 ≠ 𝑍)    &   (𝜑 → ¬ 𝑋 ∈ (𝑌𝐿𝑍))    &   (𝜑 → 𝑉 ∈ (𝑈𝐼𝑊))    ⇒   (𝜑 → ∃!𝑠 ∈ 𝑃 (⟨“𝑍𝑌𝑠”⟩ ∼ ⟨“𝑈𝑉𝑊”⟩ ∧ (𝑌 − 𝑠) = (𝑉 − 𝑈) ∧ ((𝑌𝐿𝑍) ∩ (𝑠𝐼𝑋)) ≠ ∅))
 
23-Aug-2026angmgmaddeu2 29362 Existence of a unique point for building angle addition. Case where the second angle is a zero angle. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑈 ≠ 𝑉)    &   (𝜑 → 𝑉 ≠ 𝑊)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → 𝑌 ≠ 𝑍)    &   (𝜑 → ¬ 𝑋 ∈ (𝑌𝐿𝑍))    &   (𝜑 → 𝑈((hlG‘𝐺)‘𝑉)𝑊)    ⇒   (𝜑 → ∃!𝑠 ∈ 𝑃 (⟨“𝑍𝑌𝑠”⟩ ∼ ⟨“𝑈𝑉𝑊”⟩ ∧ (𝑌 − 𝑠) = (𝑉 − 𝑈) ∧ ((𝑌𝐿𝑍) ∩ (𝑠𝐼𝑋)) ≠ ∅))
 
23-Aug-2026angmgmaddeu1 29361 There exists a unique point 𝑠 satisfying the conditions of angle addition. General case. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   𝐼 = (Itv‘𝐺)    &    − = (dist‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑈 ≠ 𝑉)    &   (𝜑 → 𝑉 ≠ 𝑊)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → 𝑌 ≠ 𝑍)    &   (𝜑 → ¬ 𝑋 ∈ (𝑌𝐿𝑍))    &   (𝜑 → ¬ 𝑈 ∈ (𝑉𝐿𝑊))    ⇒   (𝜑 → ∃!𝑠 ∈ 𝑃 (⟨“𝑍𝑌𝑠”⟩ ∼ ⟨“𝑈𝑉𝑊”⟩ ∧ (𝑌 − 𝑠) = (𝑉 − 𝑈) ∧ ((𝑌𝐿𝑍) ∩ (𝑠𝐼𝑋)) ≠ ∅))
 
23-Aug-2026elcgrabasrd 29358 Helper theorem for the membership in the base set of the angle addition monoid. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   (𝜑 → 𝑃 ∈ 𝑉)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → 𝑌 ≠ 𝑍)    ⇒   (𝜑 → ⟨“𝑋𝑌𝑍”⟩ ∈ 𝐴)
 
23-Aug-2026elcgrabasi 29357 Helper theorem for the membership in the base set of the angle addition monoid. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 ∈ V    &   𝐴 = {𝑑 ∈ (𝑃 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))}    &   (𝜑 → 𝐸 ∈ 𝐴)    ⇒   (𝜑 → ∃𝑥 ∈ 𝑃 ∃𝑦 ∈ 𝑃 ∃𝑧 ∈ 𝑃 (𝐸 = ⟨“𝑥𝑦𝑧”⟩ ∧ (𝑥 ≠ 𝑦 ∧ 𝑦 ≠ 𝑧)))
 
23-Aug-2026tgaaddcpbl2 29335 The angular addition is compatible with angle congruence: by adding congruent angles together, we obtain congruent angles. Compared with tgaaddcpbl 29334, this version handles cases where 𝑈, 𝑉 and 𝑊 are aligned. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑆 ∈ 𝑃)    &   (𝜑 → 𝑇 ∈ 𝑃)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑌 ≠ 𝑆)    &   (𝜑 → 𝑉 ≠ 𝑇)    &   (𝜑 → ((𝑌𝐿𝑆) ∩ (𝑋𝐼𝑍)) ≠ ∅)    &   (𝜑 → ((𝑉𝐿𝑇) ∩ (𝑈𝐼𝑊)) ≠ ∅)    &   (𝜑 → ⟨“𝑋𝑌𝑆”⟩ ∼ ⟨“𝑈𝑉𝑇”⟩)    &   (𝜑 → ⟨“𝑆𝑌𝑍”⟩ ∼ ⟨“𝑇𝑉𝑊”⟩)    ⇒   (𝜑 → ⟨“𝑋𝑌𝑍”⟩ ∼ ⟨“𝑈𝑉𝑊”⟩)
 
23-Aug-2026zerocgra 29313 Zero angles are congruent. Zero angles, that is, angles of degree zero, can be expressed by stating that points 𝐴 and 𝐶 are on the same ray starting at 𝐵, that is, 𝐴(𝐾‘𝐵)𝐶. See also flatcgra 29314. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝐾 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴(𝐾‘𝐵)𝐶)    &   (𝜑 → 𝐷(𝐾‘𝐸)𝐹)    &   (𝜑 → 𝐵 ∈ 𝑃)    &   (𝜑 → 𝐸 ∈ 𝑃)    ⇒   (𝜑 → ⟨“𝐴𝐵𝐶”⟩ ∼ ⟨“𝐷𝐸𝐹”⟩)
 
23-Aug-2026lnoppinn0 29213 The segment between two points 𝑋 and 𝑌 on opposite sides of a line 𝐷 intersects 𝐷. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ 𝐷) ∧ 𝑏 ∈ (𝑃 ∖ 𝐷)) ∧ ∃𝑡 ∈ 𝐷 𝑡 ∈ (𝑎𝐼𝑏))}    &   (𝜑 → 𝐺 ∈ 𝑉)    &   (𝜑 → 𝐷 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑋𝑂𝑌)    ⇒   (𝜑 → (𝐷 ∩ (𝑋𝐼𝑌)) ≠ ∅)
 
23-Aug-2026tghlsub 29068 Removing identical parts from the end of a ray segment preserves congruence. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &    − = (dist‘𝐺)    &   𝐾 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐵 ∈ 𝑃)    &   (𝜑 → 𝐸 ∈ 𝑃)    &   (𝜑 → 𝐴(𝐾‘𝐵)𝐶)    &   (𝜑 → 𝐷(𝐾‘𝐸)𝐹)    &   (𝜑 → (𝐵 − 𝐶) = (𝐸 − 𝐹))    &   (𝜑 → (𝐵 − 𝐴) = (𝐸 − 𝐷))    ⇒   (𝜑 → (𝐶 − 𝐴) = (𝐹 − 𝐷))
 
23-Aug-2026tgsegconeu 28931 The point constructed in axtgsegcon 28908 is unique. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑃 = (Base‘𝐺)    &    − = (dist‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝐴 ∈ 𝑃)    &   (𝜑 → 𝐵 ∈ 𝑃)    &   (𝜑 → 𝑋 ≠ 𝑌)    ⇒   (𝜑 → ∃!𝑧 ∈ 𝑃 (𝑌 ∈ (𝑋𝐼𝑧) ∧ (𝑌 − 𝑧) = (𝐴 − 𝐵)))
 
23-Aug-2026dfric2 20737 Alternate definition of the ring isomorphism relation. (Contributed by Jeff Madsen, 16-Jun-2011.) (Revised by AV, 23-Aug-2026.)
≃𝑟 = {⟨𝑟, 𝑠⟩ ∣ ((𝑟 ∈ Ring ∧ 𝑠 ∈ Ring) ∧ ∃𝑓 𝑓 ∈ (𝑟 RingIso 𝑠))}
 
23-Aug-2026s3rexrd 15082 Converse of s3rex 15081, deduction form. (Contributed by Thierry Arnoux, 23-Aug-2026.)
(𝜑 → 𝑆 ∈ 𝑉)    &   (𝜑 → 𝑋 ∈ 𝑆)    &   (𝜑 → 𝑌 ∈ 𝑆)    &   (𝜑 → 𝑍 ∈ 𝑆)    ⇒   (𝜑 → ⟨“𝑋𝑌𝑍”⟩ ∈ (𝑆 ↑m (0..^3)))
 
23-Aug-2026s3rex 15081 Membership in a family of words of length 3. (Contributed by Thierry Arnoux, 23-Aug-2026.)
𝑆 ∈ V    ⇒   (𝐴 ∈ (𝑆 ↑m (0..^3)) ↔ ∃𝑥 ∈ 𝑆 ∃𝑦 ∈ 𝑆 ∃𝑧 ∈ 𝑆 𝐴 = ⟨“𝑥𝑦𝑧”⟩)
 
23-Aug-2026elrelb 5775 A member of a relation expressed by an ordered pair. (Contributed by AV, 23-Aug-2026.)
(Rel 𝑅 → (𝐴 ∈ 𝑅 ↔ ∃𝑥∃𝑦(𝐴 = ⟨𝑥, 𝑦⟩ ∧ 𝑥𝑅𝑦)))
 
21-Aug-2026dfprop 38615 The set of sentences of propositional calculus is equal to the set of sentences that are either a variable encoded as a natural number, a negation of a sentence propositional calculus, or an implication between two sentences of propositional calculus. (Contributed by Thomas van Maaren, 21-Aug-2026.)
PROP = {𝑥 ∣ (∃𝑧 ∈ PROP (𝑥 = (prop¬‘𝑧) ∨ ∃𝑤 ∈ PROP 𝑥 = (𝑤prop→𝑧)) ∨ ∃𝑛 ∈ ℕ 𝑥 = (propvar ‘𝑛))}
 
21-Aug-2026dfprop2 38614 Every sentence of propositional calculus is either a variable encoded as a natural number, a negation of a sentence of propositional calculus, or an implication between two sentences of propositional calculus. (Contributed by Thomas van Maaren, 21-Aug-2026.)
PROP ⊆ {𝑥 ∣ (∃𝑧 ∈ PROP (𝑥 = (prop¬‘𝑧) ∨ ∃𝑤 ∈ PROP 𝑥 = (𝑤prop→𝑧)) ∨ ∃𝑛 ∈ ℕ 𝑥 = (propvar ‘𝑛))}
 
21-Aug-2026dfprop1 38613 The set of variables encoded as a natural number, negations of sentences of propositional calculus, and implications between sentences of propositional calculus is a subset of PROP. (Contributed by Thomas van Maaren, 21-Aug-2026.)
{𝑥 ∣ (∃𝑧 ∈ PROP (𝑥 = (prop¬‘𝑧) ∨ ∃𝑤 ∈ PROP 𝑥 = (𝑤prop→𝑧)) ∨ ∃𝑛 ∈ ℕ 𝑥 = (propvar ‘𝑛))} ⊆ PROP
 
21-Aug-2026impprop 38612 The implication between two sentences of propositional calculus is a sentence of propositional calculus. (Contributed by Thomas van Maaren, 21-Aug-2026.)
((𝑥 ∈ PROP ∧ 𝑦 ∈ PROP) → (𝑥prop→𝑦) ∈ PROP)
 
21-Aug-2026negprop 38611 The negation of a sentence of propositional calculus is a sentence of propositional calculus. (Contributed by Thomas van Maaren, 21-Aug-2026.)
(𝑥 ∈ PROP → (prop¬‘𝑥) ∈ PROP)
 
21-Aug-2026varprop 38610 Variables encoded as natural numbers are sentences of propositional calculus. (Contributed by Thomas van Maaren, 21-Aug-2026.)
(𝑛 ∈ ℕ → (propvar ‘𝑛) ∈ PROP)
 
21-Aug-2026dfproplem 38609 Given a set A, the set of all variables encoded as natural numbers, negations of elements in A, and implications between elements of A forms a set. This lemma is used when using fvmptd 6993 on the defining function of PROP. (Contributed by Thomas van Maaren, 21-Aug-2026.)
𝐴 ∈ V    ⇒   {𝑥 ∣ (∃𝑧 ∈ 𝐴 (𝑥 = (prop¬‘𝑧) ∨ ∃𝑤 ∈ 𝐴 𝑥 = (𝑤prop→𝑧)) ∨ ∃𝑛 ∈ ℕ 𝑥 = (propvar ‘𝑛))} ∈ V
 
21-Aug-2026df-prop 38608 Define the language of propositional calculus. This definition is noncircular. For a more usable and intuitive, but circular, definition see dfprop 38615. (Contributed by Thomas van Maaren, 21-Aug-2026.)
PROP = setrecs((𝑦 ∈ V ↦ {𝑥 ∣ (∃𝑧 ∈ 𝑦 (𝑥 = (prop¬‘𝑧) ∨ ∃𝑤 ∈ 𝑦 𝑥 = (𝑤prop→𝑧)) ∨ ∃𝑛 ∈ ℕ 𝑥 = (propvar ‘𝑛))}))
 
21-Aug-2026df-propimp 38606 The implication between two sentences of propositional calculus is encoded by concatenating the two sentences and appending a two at the end. (Contributed by Thomas van Maaren, 21-Aug-2026.)
prop→ = (𝑥 ∈ V, 𝑦 ∈ V ↦ ((𝑥 ++ 𝑦) ++ ⟨“2”⟩))
 
21-Aug-2026df-propneg 38605 The negation of a sentence of propositional calculus is encoded by appending a one after the sentence. (Contributed by Thomas van Maaren, 21-Aug-2026.)
prop¬ = (𝑥 ∈ V ↦ (𝑥 ++ ⟨“1”⟩))
 
21-Aug-2026df-propvar 38604 Variables in sentences of propositional calculus are encoded by appending a zero after the number of the variable. (Contributed by Thomas van Maaren, 21-Aug-2026.)
propvar = (𝑛 ∈ ℕ ↦ (⟨“𝑛”⟩ ++ ⟨“0”⟩))
 
21-Aug-2026degenmgm2 19120 A degenerate magma: although the operation is not defined for all pairs of elements of the base set, and its domain is not (a subset of) the base set, and the operation is not a function (see degenmgm2nfun 19119), the structure 𝑀 is still a magma according to our definition. (Contributed by AV, 21-Aug-2026.)
𝑀 = {⟨(Base‘ndx), {∅, 1o}⟩, ⟨(+g‘ndx), {⟨⟨1o, 1o⟩, 1o⟩, ⟨⟨1o, 2o⟩, 1o⟩, ⟨⟨1o, 2o⟩, 2o⟩}⟩}    ⇒   𝑀 ∈ Mgm
 
21-Aug-2026degenmgm2nfun 19119 The operation of a second degenerate magma is not a function. (Contributed by AV, 21-Aug-2026.)
𝑀 = {⟨(Base‘ndx), {∅, 1o}⟩, ⟨(+g‘ndx), {⟨⟨1o, 1o⟩, 1o⟩, ⟨⟨1o, 2o⟩, 1o⟩, ⟨⟨1o, 2o⟩, 2o⟩}⟩}    ⇒    ¬ Fun (+g‘𝑀)
 
21-Aug-2026degenmgm2opdm 19118 The domain of the operation of a second degenerate magma. (Contributed by AV, 21-Aug-2026.)
𝑀 = {⟨(Base‘ndx), {∅, 1o}⟩, ⟨(+g‘ndx), {⟨⟨1o, 1o⟩, 1o⟩, ⟨⟨1o, 2o⟩, 1o⟩, ⟨⟨1o, 2o⟩, 2o⟩}⟩}    ⇒   dom (+g‘𝑀) = ({1o} × {1o, 2o})
 
21-Aug-2026degenmgmnfn 19116 The operation of a degenerate magma is not a function on its base set. (Contributed by AV, 21-Aug-2026.)
𝑀 = {⟨(Base‘ndx), {∅, 1o}⟩, ⟨(+g‘ndx), {⟨⟨1o, 1o⟩, 1o⟩, ⟨⟨1o, 2o⟩, 1o⟩, ⟨⟨1o, ∅⟩, 1o⟩}⟩}    &   𝐵 = (Base‘𝑀)    ⇒    ¬ (+g‘𝑀) Fn (𝐵 × 𝐵)
 
21-Aug-2026degenmgmbas 19115 The base set of a degenerate magma. (Contributed by AV, 21-Aug-2026.)
𝑀 = {⟨(Base‘ndx), {∅, 1o}⟩, ⟨(+g‘ndx), {⟨⟨1o, 1o⟩, 1o⟩, ⟨⟨1o, 2o⟩, 1o⟩, ⟨⟨1o, ∅⟩, 1o⟩}⟩}    &   𝐵 = (Base‘𝑀)    ⇒   𝐵 = {∅, 1o}
 
21-Aug-2026xpsnprg 7135 The Cartesian product of a singleton and an unordered pair. (Contributed by AV, 21-Aug-2026.)
((𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑊 ∧ 𝐶 ∈ 𝑈) → ({𝐴} × {𝐵, 𝐶}) = {⟨𝐴, 𝐵⟩, ⟨𝐴, 𝐶⟩})
 
19-Aug-2026veroquadmodzerod 50928 The columns of the Veronese matrix, weighted by the coefficients 𝐾, sum to the zero vector of ℝfld freeLMod (1...6). (Contributed by Jiamin Zhao, 19-Aug-2026.)
𝑉 = (𝑖 ∈ (1...6), 𝑗 ∈ (1...6) ↦ ((veronese‘(𝐴‘𝑖))‘𝑗))    &   (𝜑 → 𝐴:(1...6)⟶(ℝ ↑m (1...3)))    &   (𝜑 → 𝐾:(1...6)⟶ℝ)    &   ((𝜑 ∧ 𝑖 ∈ (1...6)) → (((((𝐾‘1) · (((𝐴‘𝑖)‘1)↑2)) + ((𝐾‘2) · (((𝐴‘𝑖)‘2)↑2))) + ((𝐾‘3) · (((𝐴‘𝑖)‘3)↑2))) + ((((𝐾‘4) · (((𝐴‘𝑖)‘1) · ((𝐴‘𝑖)‘2))) + ((𝐾‘5) · (((𝐴‘𝑖)‘2) · ((𝐴‘𝑖)‘3)))) + ((𝐾‘6) · (((𝐴‘𝑖)‘3) · ((𝐴‘𝑖)‘1))))) = 0)    ⇒   (𝜑 → ((ℝfld freeLMod (1...6)) Σg (𝐾 ∘f ( ·𝑠 ‘(ℝfld freeLMod (1...6)))curry tpos 𝑉)) = (0g‘(ℝfld freeLMod (1...6))))
 
19-Aug-2026veroquadgsumlem 50927 Lemma for veroquadmodzerod 50928. Express the common homogeneous quadratic equation in ℝfld Σg form using the Veronese matrix 𝑉. (Contributed by Jiamin Zhao, 19-Aug-2026.)
𝑉 = (𝑖 ∈ (1...6), 𝑗 ∈ (1...6) ↦ ((veronese‘(𝐴‘𝑖))‘𝑗))    &   (𝜑 → 𝐴:(1...6)⟶(ℝ ↑m (1...3)))    &   (𝜑 → 𝐾:(1...6)⟶ℝ)    &   ((𝜑 ∧ 𝑖 ∈ (1...6)) → (((((𝐾‘1) · (((𝐴‘𝑖)‘1)↑2)) + ((𝐾‘2) · (((𝐴‘𝑖)‘2)↑2))) + ((𝐾‘3) · (((𝐴‘𝑖)‘3)↑2))) + ((((𝐾‘4) · (((𝐴‘𝑖)‘1) · ((𝐴‘𝑖)‘2))) + ((𝐾‘5) · (((𝐴‘𝑖)‘2) · ((𝐴‘𝑖)‘3)))) + ((𝐾‘6) · (((𝐴‘𝑖)‘3) · ((𝐴‘𝑖)‘1))))) = 0)    ⇒   ((𝜑 ∧ 𝑖 ∈ (1...6)) → (ℝfld Σg (𝑗 ∈ (1...6) ↦ ((𝐾‘𝑗) · ((curry 𝑉‘𝑖)‘𝑗)))) = 0)
 
19-Aug-2026veronesematrowexpd 50926 Currying the Veronese matrix gives the indexed family of Veronese images, with each image expressed explicitly by coordinates. (Contributed by Jiamin Zhao, 19-Aug-2026.)
𝑉 = (𝑖 ∈ (1...6), 𝑗 ∈ (1...6) ↦ ((veronese‘(𝐴‘𝑖))‘𝑗))    &   (𝜑 → 𝐴:(1...6)⟶(ℝ ↑m (1...3)))    ⇒   (𝜑 → curry 𝑉 = (𝑖 ∈ (1...6) ↦ (𝑘 ∈ (1...6) ↦ if(𝑘 = 1, (((𝐴‘𝑖)‘1)↑2), if(𝑘 = 2, (((𝐴‘𝑖)‘2)↑2), if(𝑘 = 3, (((𝐴‘𝑖)‘3)↑2), if(𝑘 = 4, (((𝐴‘𝑖)‘1) · ((𝐴‘𝑖)‘2)), if(𝑘 = 5, (((𝐴‘𝑖)‘2) · ((𝐴‘𝑖)‘3)), (((𝐴‘𝑖)‘3) · ((𝐴‘𝑖)‘1))))))))))
 
19-Aug-2026veronesematrowd 50925 Currying the Veronese matrix gives the indexed family of Veronese images of the points 𝐴‘𝑖. (Contributed by Jiamin Zhao, 19-Aug-2026.)
𝑉 = (𝑖 ∈ (1...6), 𝑗 ∈ (1...6) ↦ ((veronese‘(𝐴‘𝑖))‘𝑗))    &   (𝜑 → 𝐴:(1...6)⟶(ℝ ↑m (1...3)))    ⇒   (𝜑 → curry 𝑉 = (𝑖 ∈ (1...6) ↦ (veronese‘(𝐴‘𝑖))))
 
19-Aug-2026veronesematbasd 50924 The matrix whose 𝑖-th row is the Veronese image of 𝐴‘𝑖 belongs to the base set of (1...6) Mat ℝfld. (Contributed by Jiamin Zhao, 19-Aug-2026.)
𝑉 = (𝑖 ∈ (1...6), 𝑗 ∈ (1...6) ↦ ((veronese‘(𝐴‘𝑖))‘𝑗))    &   (𝜑 → 𝐴:(1...6)⟶(ℝ ↑m (1...3)))    ⇒   (𝜑 → 𝑉 ∈ (Base‘((1...6) Mat ℝfld)))
 
19-Aug-2026veronesefvcl 50916 Every coordinate of the Veronese map of a real 3-vector is real. (Contributed by Jiamin Zhao, 19-Aug-2026.)
((𝑄 ∈ (ℝ ↑m (1...3)) ∧ 𝐾 ∈ (1...6)) → ((veronese‘𝑄)‘𝐾) ∈ ℝ)
 
19-Aug-2026omeiunle 47471 The outer measure of the indexed union of a countable set is less than or equal to the extended sum of the outer measures. The proof uses abrexct 23753 rather than fnrndomg 10599, and so does not require ax-ac 10518. (Contributed by Glauco Siliprandi, 17-Aug-2020.) (Revised by Vincent Gonzalez, 19-Aug-2026.)
Ⅎ𝑛𝜑    &   Ⅎ𝑛𝐸    &   (𝜑 → 𝑂 ∈ OutMeas)    &   𝑋 = ∪ dom 𝑂    &   𝑍 = (ℤ≥‘𝑁)    &   (𝜑 → 𝐸:𝑍⟶𝒫 𝑋)    ⇒   (𝜑 → (𝑂‘∪ 𝑛 ∈ 𝑍 (𝐸‘𝑛)) ≤ (Σ^‘(𝑛 ∈ 𝑍 ↦ (𝑂‘(𝐸‘𝑛)))))
 
19-Aug-2026disjinfi 46150 Only a finite number of disjoint sets can have a nonempty intersection with a finite set 𝐶. The proof uses fodomfi 9288 rather than fodomg 10581, and so does not require ax-ac 10518. (Contributed by Glauco Siliprandi, 17-Aug-2020.) (Revised by Vincent Gonzalez, 19-Aug-2026.)
((𝜑 ∧ 𝑥 ∈ 𝐴) → 𝐵 ∈ 𝑉)    &   (𝜑 → Disj 𝑥 ∈ 𝐴 𝐵)    &   (𝜑 → 𝐶 ∈ Fin)    ⇒   (𝜑 → {𝑥 ∈ 𝐴 ∣ (𝐵 ∩ 𝐶) ≠ ∅} ∈ Fin)
 
19-Aug-2026sigaclci 34746 A sigma-algebra is closed under countable intersections. Deduction version. The proof uses abrexct 23753 rather than abrexdom2jm 33086, and so does not require ax-ac 10518. (Contributed by Thierry Arnoux, 19-Sep-2016.) (Revised by Vincent Gonzalez, 19-Aug-2026.)
(((𝑆 ∈ ∪ ran sigAlgebra ∧ 𝐴 ∈ 𝒫 𝑆) ∧ (𝐴 ≼ ω ∧ 𝐴 ≠ ∅)) → ∩ 𝐴 ∈ 𝑆)
 
19-Aug-2026madefi 28281 The made set of an ordinal natural is finite. (Contributed by Scott Fenton, 20-Aug-2025.) (Proof shortened by Vincent Gonzalez, 19-Aug-2026.)
(𝐴 ∈ ω → ( M ‘𝐴) ∈ Fin)
 
18-Aug-2026degenmgm 19117 A degenerate magma: although the operation is not defined for all pairs of elements of the base set ((∅(+g‘𝑀)1o) and (∅(+g‘𝑀)∅) are not defined, and therefore are ∅ by definition, which is contained in the base set), and its domain is not (a subset of) the base set (2o is in the domain of the operation, but not in the base set) , the structure 𝑀 is still a magma according to our definition. (Contributed by AV, 18-Aug-2026.)
𝑀 = {⟨(Base‘ndx), {∅, 1o}⟩, ⟨(+g‘ndx), {⟨⟨1o, 1o⟩, 1o⟩, ⟨⟨1o, 2o⟩, 1o⟩, ⟨⟨1o, ∅⟩, 1o⟩}⟩}    ⇒   𝑀 ∈ Mgm
 
18-Aug-2026degenmgmopdm 19114 The domain of the operation of a degenerate magma. (Contributed by AV, 18-Aug-2026.)
𝑀 = {⟨(Base‘ndx), {∅, 1o}⟩, ⟨(+g‘ndx), {⟨⟨1o, 1o⟩, 1o⟩, ⟨⟨1o, 2o⟩, 1o⟩, ⟨⟨1o, ∅⟩, 1o⟩}⟩}    ⇒   dom (+g‘𝑀) = ({1o} × {∅, 1o, 2o})
 
18-Aug-2026mndideu 18914 The two-sided identity element of a monoid is unique. Lemma 2.2.1(a) of [Herstein] p. 55. (Contributed by Mario Carneiro, 8-Dec-2014.) (Proof shortened by AV, 18-Aug-2026.)
𝐵 = (Base‘𝐺)    &    + = (+g‘𝐺)    ⇒   (𝐺 ∈ Mnd → ∃!𝑢 ∈ 𝐵 ∀𝑥 ∈ 𝐵 ((𝑢 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑢) = 𝑥))
 
18-Aug-2026mgmideud 18819 Uniqueness of the left and right identity element of a magma when it exists. (Contributed by FL, 12-Dec-2009.) (Revised by Mario Carneiro, 22-Dec-2013.) (Revised by AV, 18-Aug-2026.)
(𝜑 → ∃𝑢 ∈ 𝐵 ∀𝑥 ∈ 𝐵 ((𝑢 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑢) = 𝑥))    ⇒   (𝜑 → ∃!𝑢 ∈ 𝐵 ∀𝑥 ∈ 𝐵 ((𝑢 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑢) = 𝑥))
 
18-Aug-2026fvtp0 7198 The undefined value of a function with a domain of three elements. (Contributed by AV, 18-Aug-2026.)
𝐷 ∈ V    &   𝐸 ∈ V    &   𝐹 ∈ V    &   𝑋 ∈ V    ⇒   ((𝑋 ≠ 𝐴 ∧ 𝑋 ≠ 𝐵 ∧ 𝑋 ≠ 𝐶) → ({⟨𝐴, 𝐷⟩, ⟨𝐵, 𝐸⟩, ⟨𝐶, 𝐹⟩}‘𝑋) = ∅)
 
18-Aug-2026xpsntpg 7136 The Cartesian product of a singleton and an unordered triple. (Contributed by AV, 18-Aug-2026.)
(((𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑊) ∧ (𝐶 ∈ 𝑈 ∧ 𝐷 ∈ 𝑇)) → ({𝐴} × {𝐵, 𝐶, 𝐷}) = {⟨𝐴, 𝐵⟩, ⟨𝐴, 𝐶⟩, ⟨𝐴, 𝐷⟩})
 
17-Aug-2026veronesevrowd 50923 The Veronese map at a point, expressed explicitly as a piecewise maps-to function on the six coordinates. (Contributed by Jiamin Zhao, 17-Aug-2026.)
(𝜑 → 𝑃 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → (veronese‘𝑃) = (𝑘 ∈ (1...6) ↦ if(𝑘 = 1, ((𝑃‘1)↑2), if(𝑘 = 2, ((𝑃‘2)↑2), if(𝑘 = 3, ((𝑃‘3)↑2), if(𝑘 = 4, ((𝑃‘1) · (𝑃‘2)), if(𝑘 = 5, ((𝑃‘2) · (𝑃‘3)), ((𝑃‘3) · (𝑃‘1)))))))))
 
17-Aug-2026veronesev6lem 50922 Lemma for veronesevrowd 50923. Value of the sixth coordinate of the Veronese map at a point. (Contributed by Jiamin Zhao, 17-Aug-2026.)
(𝜑 → 𝑃 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → ((veronese‘𝑃)‘6) = ((𝑃‘3) · (𝑃‘1)))
 
17-Aug-2026veronesev5lem 50921 Lemma for veronesevrowd 50923. Value of the fifth coordinate of the Veronese map at a point. (Contributed by Jiamin Zhao, 17-Aug-2026.)
(𝜑 → 𝑃 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → ((veronese‘𝑃)‘5) = ((𝑃‘2) · (𝑃‘3)))
 
17-Aug-2026veronesev4lem 50920 Lemma for veronesevrowd 50923. Value of the fourth coordinate of the Veronese map at a point. (Contributed by Jiamin Zhao, 17-Aug-2026.)
(𝜑 → 𝑃 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → ((veronese‘𝑃)‘4) = ((𝑃‘1) · (𝑃‘2)))
 
17-Aug-2026veronesev3lem 50919 Lemma for veronesevrowd 50923. Value of the third coordinate of the Veronese map at a point. (Contributed by Jiamin Zhao, 17-Aug-2026.)
(𝜑 → 𝑃 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → ((veronese‘𝑃)‘3) = ((𝑃‘3)↑2))
 
17-Aug-2026difelsiga 34749 A sigma-algebra is closed under class differences. The proof goes through difunielsiga 34747 and unelsiga 34748 rather than countable intersection, and so does not use ax-ac 10518. (Contributed by Thierry Arnoux, 13-Sep-2016.) (Proof shortened by Vincent Gonzalez, 17-Aug-2026.)
((𝑆 ∈ ∪ ran sigAlgebra ∧ 𝐴 ∈ 𝑆 ∧ 𝐵 ∈ 𝑆) → (𝐴 ∖ 𝐵) ∈ 𝑆)
 
17-Aug-2026difunielsiga 34747 A sigma-algebra is closed under complement relative to its base set. This is immediate from the definition, see issiga 34726, but the library states it nowhere in this form. (Contributed by Vincent Gonzalez, 17-Aug-2026.)
((𝑆 ∈ ∪ ran sigAlgebra ∧ 𝐴 ∈ 𝑆) → (∪ 𝑆 ∖ 𝐴) ∈ 𝑆)
 
17-Aug-2026mndfo 18928 The addition operation of a monoid is an onto function (assuming it is a function). (Contributed by Mario Carneiro, 11-Oct-2013.) (Proof shortened by AV, 17-Aug-2026.)
𝐵 = (Base‘𝐺)    &    + = (+g‘𝐺)    ⇒   ((𝐺 ∈ Mnd ∧ + Fn (𝐵 × 𝐵)) → + :(𝐵 × 𝐵)–onto→𝐵)
 
17-Aug-2026mndpfo 18927 The addition operation of a monoid as a function is an onto function. (Contributed by FL, 2-Nov-2009.) (Revised by Mario Carneiro, 11-Oct-2013.) (Revised by AV, 23-Jan-2020.) (Proof shortened by AV, 17-Aug-2026.)
𝐵 = (Base‘𝐺)    &    ⨣ = (+𝑓‘𝐺)    ⇒   (𝐺 ∈ Mnd → ⨣ :(𝐵 × 𝐵)–onto→𝐵)
 
17-Aug-2026fnrndomg 10599 The range of a function is dominated by its domain. This theorem requires the axiom of choice ax-ac2 10522; see fnrndomnum 10598 for a version that does not. (Contributed by NM, 1-Sep-2004.) (Proof shortened by Vincent Gonzalez, 17-Aug-2026.)
(𝐴 ∈ 𝐵 → (𝐹 Fn 𝐴 → ran 𝐹 ≼ 𝐴))
 
17-Aug-2026fnrndomnum 10598 A version of fnrndomg 10599 that does not require the axiom of choice ax-ac 10518. (Contributed by Vincent Gonzalez, 17-Aug-2026.)
(𝐴 ∈ dom card → (𝐹 Fn 𝐴 → ran 𝐹 ≼ 𝐴))
 
16-Aug-2026veronesev2lem 50918 Lemma for veronesevrowd 50923. Value of the second coordinate of the Veronese map at a point. (Contributed by Jiamin Zhao, 16-Aug-2026.)
(𝜑 → 𝑃 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → ((veronese‘𝑃)‘2) = ((𝑃‘2)↑2))
 
16-Aug-2026mgmfod 18839 The operation of a magma with identity is an onto function (assuming it is a function). (Contributed by FL, 2-Nov-2009.) (Revised by AV, 16-Aug-2026.)
𝐵 = (Base‘𝐺)    &    + = (+g‘𝐺)    &   (𝜑 → 𝐺 ∈ Mgm)    &   (𝜑 → ∃𝑒 ∈ 𝐵 ∀𝑥 ∈ 𝐵 ((𝑒 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑒) = 𝑥))    &   (𝜑 → + Fn (𝐵 × 𝐵))    ⇒   (𝜑 → + :(𝐵 × 𝐵)–onto→𝐵)
 
16-Aug-2026mgmidprnd 18838 Range of an operation with a left and right identity element. (Contributed by FL, 2-Nov-2009.) (Revised by AV, 16-Aug-2026.)
𝐵 = (Base‘𝐺)    &    + = (+g‘𝐺)    &   (𝜑 → 𝐺 ∈ Mgm)    &   (𝜑 → ∃𝑒 ∈ 𝐵 ∀𝑥 ∈ 𝐵 ((𝑒 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑒) = 𝑥))    &    ⨣ = (+𝑓‘𝐺)    ⇒   (𝜑 → ran ⨣ = 𝐵)
 
16-Aug-2026mgmidpfod 18837 The operation of a magma with identity as a function is an onto function. (Contributed by FL, 2-Nov-2009.) (Revised by Mario Carneiro, 22-Dec-2013.) (Revised by AV, 16-Aug-2026.)
𝐵 = (Base‘𝐺)    &    + = (+g‘𝐺)    &   (𝜑 → 𝐺 ∈ Mgm)    &   (𝜑 → ∃𝑒 ∈ 𝐵 ∀𝑥 ∈ 𝐵 ((𝑒 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑒) = 𝑥))    &    ⨣ = (+𝑓‘𝐺)    ⇒   (𝜑 → ⨣ :(𝐵 × 𝐵)–onto→𝐵)
 
16-Aug-2026mgmn0plusgplusf 18808 The group addition function of a magma is the restriction of its group operation to its base set if the base set does not contain the empty set. (Contributed by AV, 16-Aug-2026.)
𝐵 = (Base‘𝐺)    &    + = (+g‘𝐺)    &   (𝜑 → 𝐺 ∈ Mgm)    &   (𝜑 → ∅ ∉ 𝐵)    &    ⨣ = (+𝑓‘𝐺)    ⇒   (𝜑 → ⨣ = ( + ↾ (𝐵 × 𝐵)))
 
16-Aug-2026mgmn0plusgf 18807 The restriction of the group operation of a magma to its base set is a function if the base set does not contain the empty set. Excluding the empty set from the base set is necessary because of the specific definition of an undefined operation value (see also ndmovcl 7598 and ndmovrcl 7599). (Contributed by AV, 16-Aug-2026.)
𝐵 = (Base‘𝐺)    &    + = (+g‘𝐺)    &   (𝜑 → 𝐺 ∈ Mgm)    &   (𝜑 → ∅ ∉ 𝐵)    &   𝑃 = ( + ↾ (𝐵 × 𝐵))    ⇒   (𝜑 → 𝑃:(𝐵 × 𝐵)⟶𝐵)
 
16-Aug-2026relresfld 6271 Restriction of a relation to its field. (Contributed by FL, 15-Apr-2012.) (Proof shortened by Eric Schmidt, 16-Aug-2026.)
(Rel 𝑅 → (𝑅 ↾ ∪ ∪ 𝑅) = 𝑅)
 
15-Aug-2026veronesev1lem 50917 Lemma for veronesevrowd 50923. Value of the first coordinate of the Veronese map at a point. (Contributed by Jiamin Zhao, 15-Aug-2026.)
(𝜑 → 𝑃 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → ((veronese‘𝑃)‘1) = ((𝑃‘1)↑2))
 
15-Aug-2026f1resfz0f1d 13907 If a function with a sequence of nonnegative integers (starting at 0) as its domain is one-to-one when 0 is removed, and if the range of that restriction does not contain the function's value at the removed integer, then the function is itself one-to-one. (Contributed by BTernaryTau, 4-Oct-2023.) (Revised by Mingli Yuan, 15-Aug-2026.)
(𝜑 → 𝐾 ∈ ℕ0)    &   (𝜑 → 𝐹:(0...𝐾)⟶𝑉)    &   (𝜑 → Fun ◡(𝐹 ↾ (1...𝐾)))    &   (𝜑 → ((𝐹 “ {0}) ∩ (𝐹 “ (1...𝐾))) = ∅)    ⇒   (𝜑 → 𝐹:(0...𝐾)–1-1→𝑉)
 
15-Aug-2026f1resrcmplf1dlem 7270 Lemma for f1resrcmplf1d 7271. (Contributed by BTernaryTau, 27-Sep-2023.) (Revised by Mingli Yuan, 15-Aug-2026.)
(𝜑 → 𝐶 ⊆ 𝐴)    &   (𝜑 → 𝐷 ⊆ 𝐴)    &   (𝜑 → 𝐹:𝐴⟶𝐵)    &   (𝜑 → ((𝐹 “ 𝐶) ∩ (𝐹 “ 𝐷)) = ∅)    &   (𝜑 → 𝑋 ∈ 𝐶)    &   (𝜑 → 𝑌 ∈ 𝐷)    &   (𝜑 → (𝐹‘𝑋) = (𝐹‘𝑌))    ⇒   (𝜑 → 𝑋 = 𝑌)
 
14-Aug-2026veronesevald 50915 Value of the Veronese map at a point, expressed as a maps-to function on the six coordinates. (Contributed by Jiamin Zhao, 14-Aug-2026.)
(𝜑 → 𝑃 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → (veronese‘𝑃) = (𝑘 ∈ (1...6) ↦ (((if(𝑘 = 1, ((𝑃‘1)↑2), 0) + if(𝑘 = 2, ((𝑃‘2)↑2), 0)) + if(𝑘 = 3, ((𝑃‘3)↑2), 0)) + ((if(𝑘 = 4, ((𝑃‘1) · (𝑃‘2)), 0) + if(𝑘 = 5, ((𝑃‘2) · (𝑃‘3)), 0)) + if(𝑘 = 6, ((𝑃‘3) · (𝑃‘1)), 0)))))
 
14-Aug-2026df-veronese 50913 Define the quadratic Veronese map on real 3-vectors, with coordinates ordered as ( x^2 , y^2 , z^2 , x y , y z , z x ). (Contributed by Jiamin Zhao, 14-Aug-2026.)
veronese = (𝑞 ∈ (ℝ ↑m (1...3)) ↦ (𝑘 ∈ (1...6) ↦ (((if(𝑘 = 1, ((𝑞‘1)↑2), 0) + if(𝑘 = 2, ((𝑞‘2)↑2), 0)) + if(𝑘 = 3, ((𝑞‘3)↑2), 0)) + ((if(𝑘 = 4, ((𝑞‘1) · (𝑞‘2)), 0) + if(𝑘 = 5, ((𝑞‘2) · (𝑞‘3)), 0)) + if(𝑘 = 6, ((𝑞‘3) · (𝑞‘1)), 0)))))
 
14-Aug-2026cveronese 50912 Extend class notation to include the quadratic Veronese map on real 3-vectors. (Contributed by Jiamin Zhao, 14-Aug-2026.)
class veronese
 
14-Aug-2026findcard4 38600 Schema for strong induction on the cardinality of a finite set. The inductive hypothesis is that the result is true on any set with less elements. The result is then proven to be true for all finite sets. (Contributed by Thomas van Maaren, 14-Aug-2026.)
(𝑥 = 𝑦 → (𝜑 ↔ 𝜒))    &   (𝑥 = 𝐴 → (𝜑 ↔ 𝜏))    &   (𝑦 ∈ Fin → (∀𝑥((♯‘𝑥) < (♯‘𝑦) → 𝜑) → 𝜒))    ⇒   (𝐴 ∈ Fin → 𝜏)
 
13-Aug-20262elfz13 50888 Membership of 2 in the integer interval ( 1 ... 3 ). (Suggested by tirix.) (Contributed by Jiamin Zhao, 1-Aug-2026.) (Proof shortened by Jiamin Zhao, 13-Aug-2026.)
2 ∈ (1...3)
 
13-Aug-20261elfz13 50887 Membership of 1 in the integer interval ( 1 ... 3 ). (Suggested by avekens.) (Contributed by Jiamin Zhao, 1-Aug-2026.) (Proof shortened by Jiamin Zhao, 13-Aug-2026.)
1 ∈ (1...3)
 
12-Aug-2026crossp3d 50911 The vector triple product expansion (BAC-CAB rule): the cross product of 𝑋 with (𝑌⊠𝑍) equals 𝑌 scaled by the dot product of 𝑋 and 𝑍, minus 𝑍 scaled by the dot product of 𝑋 and 𝑌. The dot products are written out as explicit three-term sums of component products, matching the pointwise style of df-crossp 50895 rather than introducing a separate dot product operator. (Contributed by Jiamin Zhao, 12-Aug-2026.)
(𝜑 → 𝑋 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝑌 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝑍 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → (𝑋⊠(𝑌⊠𝑍)) = (𝑘 ∈ (1...3) ↦ ((((((𝑋‘1) · (𝑍‘1)) + ((𝑋‘2) · (𝑍‘2))) + ((𝑋‘3) · (𝑍‘3))) · (𝑌‘𝑘)) − (((((𝑋‘1) · (𝑌‘1)) + ((𝑋‘2) · (𝑌‘2))) + ((𝑋‘3) · (𝑌‘3))) · (𝑍‘𝑘)))))
 
12-Aug-2026crosspaltd 50910 Antisymmetry of the cross product: swapping the two vectors negates the result. (Contributed by Jiamin Zhao, 12-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐵 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → (𝐴⊠𝐵) = (𝑘 ∈ (1...3) ↦ -((𝐵⊠𝐴)‘𝑘)))
 
12-Aug-2026crosspdotd 50909 Value of the scalar triple product, expanded into the standard six-term Sarrus polynomial. (Contributed by Jiamin Zhao, 12-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐵 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐶 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → (𝐵(tripp‘𝐴)𝐶) = (((((𝐴‘1) · (𝐵‘2)) · (𝐶‘3)) − (((𝐴‘1) · (𝐵‘3)) · (𝐶‘2))) + (((((𝐴‘2) · (𝐵‘3)) · (𝐶‘1)) − (((𝐴‘2) · (𝐵‘1)) · (𝐶‘3))) + ((((𝐴‘3) · (𝐵‘1)) · (𝐶‘2)) − (((𝐴‘3) · (𝐵‘2)) · (𝐶‘1))))))
 
12-Aug-2026crosspdotsumlem 50908 Lemma for crosspdotd 50909. Expand the group sum over (1...3) into an explicit three-term sum. (Contributed by Jiamin Zhao, 12-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐵 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐶 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → (ℝfld Σg (𝑘 ∈ (1...3) ↦ ((𝐴‘𝑘) · ((𝐵⊠𝐶)‘𝑘)))) = (((𝐴‘1) · ((𝐵⊠𝐶)‘1)) + (((𝐴‘2) · ((𝐵⊠𝐶)‘2)) + ((𝐴‘3) · ((𝐵⊠𝐶)‘3)))))
 
12-Aug-2026crosspdot0lem 50907 Lemma for crosspdotd 50909. Unfold the curried scalar triple product application into an explicit group sum. (Contributed by Jiamin Zhao, 12-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐵 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐶 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → (𝐵(tripp‘𝐴)𝐶) = (ℝfld Σg (𝑘 ∈ (1...3) ↦ ((𝐴‘𝑘) · ((𝐵⊠𝐶)‘𝑘)))))
 
12-Aug-2026crosspv3d 50906 Value of the third component of the cross product. (Contributed by Jiamin Zhao, 12-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐵 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → ((𝐴⊠𝐵)‘3) = (((𝐴‘1) · (𝐵‘2)) − ((𝐴‘2) · (𝐵‘1))))
 
12-Aug-2026crosspv2d 50905 Value of the second component of the cross product. (Contributed by Jiamin Zhao, 12-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐵 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → ((𝐴⊠𝐵)‘2) = (((𝐴‘3) · (𝐵‘1)) − ((𝐴‘1) · (𝐵‘3))))
 
12-Aug-2026crosspv1d 50904 Value of the first component of the cross product. (Contributed by Jiamin Zhao, 12-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐵 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → ((𝐴⊠𝐵)‘1) = (((𝐴‘2) · (𝐵‘3)) − ((𝐴‘3) · (𝐵‘2))))
 
12-Aug-2026crosspcld 50903 Closure of the cross product: the cross product of two 3-dimensional real coordinate vectors is again such a vector. (Contributed by Jiamin Zhao, 12-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐵 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → (𝐴⊠𝐵) ∈ (ℝ ↑m (1...3)))
 
12-Aug-2026ress0g 18934 0g is unaffected by restriction. This is a bit more generic than submnd0 18936. (Contributed by Thierry Arnoux, 23-Oct-2017.) (Proof shortened by AV, 12-Aug-2026.)
𝑆 = (𝑅 ↾s 𝐴)    &   𝐵 = (Base‘𝑅)    &    0 = (0g‘𝑅)    ⇒   ((𝑅 ∈ Mnd ∧ 0 ∈ 𝐴 ∧ 𝐴 ⊆ 𝐵) → 0 = (0g‘𝑆))
 
12-Aug-2026idressid 18842 The restriction of a structure with an identity element to a subset containing the identity element has the same identity element. (Contributed by Jeff Madsen, 8-Jun-2010.) (Revised by Mario Carneiro, 23-Dec-2013.) (Revised by AV, 12-Aug-2026.)
𝐵 = (Base‘𝐺)    &    + = (+g‘𝐺)    &    0 = (0g‘𝐺)    &   (𝜑 → ∃𝑒 ∈ 𝐵 ∀𝑥 ∈ 𝐵 ((𝑒 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑒) = 𝑥))    &   𝑆 = (𝐺 ↾s 𝐴)    &   (𝜑 → 𝐴 ⊆ 𝐵)    &   (𝜑 → 0 ∈ 𝐴)    ⇒   (𝜑 → (0g‘𝑆) = 0 )
 
11-Aug-2026crosspclem 50902 Lemma for crosspcld 50903. Closure of the three-way coordinate case split used in the cross product's mapping rule. (Contributed by Jiamin Zhao, 11-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐵 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → if(𝑘 = 1, (((𝐴‘2) · (𝐵‘3)) − ((𝐴‘3) · (𝐵‘2))), if(𝑘 = 2, (((𝐴‘3) · (𝐵‘1)) − ((𝐴‘1) · (𝐵‘3))), (((𝐴‘1) · (𝐵‘2)) − ((𝐴‘2) · (𝐵‘1))))) ∈ ℝ)
 
11-Aug-2026crosspcle3d 50901 Closure of the third component of the cross product's coordinate formula. (Contributed by Jiamin Zhao, 11-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐵 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → (((𝐴‘1) · (𝐵‘2)) − ((𝐴‘2) · (𝐵‘1))) ∈ ℝ)
 
11-Aug-2026crosspcle2d 50900 Closure of the second component of the cross product's coordinate formula. (Contributed by Jiamin Zhao, 11-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐵 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → (((𝐴‘3) · (𝐵‘1)) − ((𝐴‘1) · (𝐵‘3))) ∈ ℝ)
 
11-Aug-2026crosspcle1d 50899 Closure of the first component of the cross product's coordinate formula. (Contributed by Jiamin Zhao, 11-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    &   (𝜑 → 𝐵 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → (((𝐴‘2) · (𝐵‘3)) − ((𝐴‘3) · (𝐵‘2))) ∈ ℝ)
 
11-Aug-2026wrdf1d 50884 A one-to-one word maps its domain into its alphabet. (Contributed by Mingli Yuan, 11-Aug-2026.)
(𝜑 → 𝑊 ∈ Word 𝐷)    &   (𝜑 → Fun ◡𝑊)    ⇒   (𝜑 → 𝑊:dom 𝑊–1-1→𝐷)
 
11-Aug-2026idressidex 18841 The restriction of a structure with an identity element to a subset containing the identity element has an identity element. (Contributed by Jeff Madsen, 8-Jun-2010.) (Revised by Mario Carneiro, 23-Dec-2013.) (Revised by AV, 11-Aug-2026.)
𝐵 = (Base‘𝐺)    &    + = (+g‘𝐺)    &    0 = (0g‘𝐺)    &   (𝜑 → ∃𝑒 ∈ 𝐵 ∀𝑥 ∈ 𝐵 ((𝑒 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑒) = 𝑥))    &   𝑆 = (𝐺 ↾s 𝐴)    &   (𝜑 → 𝐴 ⊆ 𝐵)    &   (𝜑 → 0 ∈ 𝐴)    ⇒   (𝜑 → ∃𝑒 ∈ 𝐴 ∀𝑥 ∈ 𝐴 ((𝑒 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑒) = 𝑥))
 
11-Aug-2026idressidex0 18840 The restriction of a structure with an identity element to a subset containing the identity element has an identity element. (Contributed by Jeff Madsen, 8-Jun-2010.) (Revised by Mario Carneiro, 23-Dec-2013.) (Revised by AV, 11-Aug-2026.)
𝐵 = (Base‘𝐺)    &    + = (+g‘𝐺)    &    0 = (0g‘𝐺)    &   (𝜑 → ∃𝑒 ∈ 𝐵 ∀𝑥 ∈ 𝐵 ((𝑒 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑒) = 𝑥))    &   𝑆 = (𝐺 ↾s 𝐴)    &   (𝜑 → 𝐴 ⊆ 𝐵)    &   (𝜑 → 0 ∈ 𝐴)    &   𝐶 = (Base‘𝑆)    ⇒   (𝜑 → ∃𝑒 ∈ 𝐶 ∀𝑥 ∈ 𝐶 ((𝑒 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑒) = 𝑥))
 
11-Aug-20260gisid 18828 In a structure with an identity element, the group identity element is an identity element of the structure. (Contributed by Jeff Madsen, 8-Jun-2010.) (Revised by Mario Carneiro, 23-Dec-2013.) (Revised by AV, 11-Aug-2026.)
𝐵 = (Base‘𝐺)    &    0 = (0g‘𝐺)    &    + = (+g‘𝐺)    &   (𝜑 → ∃𝑒 ∈ 𝐵 ∀𝑥 ∈ 𝐵 ((𝑒 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑒) = 𝑥))    ⇒   (𝜑 → ( 0 ∈ 𝐵 ∧ ∀𝑥 ∈ 𝐵 (( 0 + 𝑥) = 𝑥 ∧ (𝑥 + 0 ) = 𝑥)))
 
10-Aug-2026rr3fv3cld 50893 Third component of a 3-dimensional real coordinate vector is real. (Contributed by Jiamin Zhao, 10-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → (𝐴‘3) ∈ ℝ)
 
10-Aug-2026rr3fv2cld 50892 Second component of a 3-dimensional real coordinate vector is real. (Contributed by Jiamin Zhao, 10-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → (𝐴‘2) ∈ ℝ)
 
10-Aug-2026rr3fv1cld 50891 First component of a 3-dimensional real coordinate vector is real. (Contributed by Jiamin Zhao, 10-Aug-2026.)
(𝜑 → 𝐴 ∈ (ℝ ↑m (1...3)))    ⇒   (𝜑 → (𝐴‘1) ∈ ℝ)
 
10-Aug-2026had0 1634 If the first input is false, then the adder sum is equivalent to the exclusive disjunction of the other two inputs, and conversely. (Contributed by Mario Carneiro, 4-Sep-2016.) (Proof shortened by Wolf Lammen, 12-Jul-2020.) Strengthen to a biconditional. (Revised by BJ, 10-Aug-2026.)
(¬ 𝜑 ↔ (hadd(𝜑, 𝜓, 𝜒) ↔ (𝜓 ⊻ 𝜒)))
 
10-Aug-2026had1 1633 If the first input is true, then the adder sum is equivalent to the biconditionality of the other two inputs, and conversely. (Contributed by Mario Carneiro, 4-Sep-2016.) (Proof shortened by Wolf Lammen, 11-Jul-2020.) Strengthen to a biconditional. (Revised by BJ, 10-Aug-2026.)
(𝜑 ↔ (hadd(𝜑, 𝜓, 𝜒) ↔ (𝜓 ↔ 𝜒)))
 
10-Aug-2026birot 389 Rotation of the arguments of the nested implication (. ↔ (. ↔ .)) (a general phenomenon for a commutative associative binary operation, see e.g., inrot 4178) . (Contributed by BJ, 10-Aug-2026.)
((𝜑 ↔ (𝜓 ↔ 𝜒)) ↔ (𝜓 ↔ (𝜒 ↔ 𝜑)))
 
8-Aug-2026dfring2 20497 The predicate "is a unital ring" based on a ring being abelian. Definition of "ring with unit" in [Lang] p. 83. (Contributed by Jeff Hankins, 21-Nov-2006.) (Revised by AV, 8-Aug-2026.)
𝐵 = (Base‘𝑅)    &    · = (.r‘𝑅)    &   𝐺 = (mulGrp‘𝑅)    &    + = (+g‘𝑅)    ⇒   (𝑅 ∈ Ring ↔ (𝑅 ∈ Abel ∧ 𝐺 ∈ Mnd ∧ ∀𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐵 ∀𝑧 ∈ 𝐵 ((𝑥 · (𝑦 + 𝑧)) = ((𝑥 · 𝑦) + (𝑥 · 𝑧)) ∧ ((𝑥 + 𝑦) · 𝑧) = ((𝑥 · 𝑧) + (𝑦 · 𝑧)))))
 
8-Aug-2026relcnvtrg 6261 Subclass law for converse of a composition. A particular case is ((𝑅 ∘ 𝑅) ⊆ 𝑅 ↔ (◡𝑅 ∘ ◡𝑅) ⊆ ◡𝑅), which says that a relation is transitive iff its converse is transitive. (Contributed by FL, 19-Sep-2011.) Generalize to a statement about three classes rather than one. (Revised by Peter Mazsa, 17-Oct-2023.) Remove antecedent. (Revised by Eric Schmidt, 8-Aug-2026.)
((𝑅 ∘ 𝑆) ⊆ 𝑇 ↔ (◡𝑆 ∘ ◡𝑅) ⊆ ◡𝑇)
 
5-Aug-2026f1owe 7353 Well-ordering of isomorphic relations. (Contributed by NM, 4-Mar-1997.) Strengthen to biconditional. (Revised by Eric Schmidt, 5-Aug-2026.)
𝑅 = {⟨𝑥, 𝑦⟩ ∣ (𝐹‘𝑥)𝑆(𝐹‘𝑦)}    ⇒   (𝐹:𝐴–1-1-onto→𝐵 → (𝑅 We 𝐴 ↔ 𝑆 We 𝐵))
 
4-Aug-2026f1we 7355 Pull back a well ordering by a one-to-one function. (Contributed by Eric Schmidt, 4-Aug-2026.)
𝑅 = {⟨𝑥, 𝑦⟩ ∣ (𝐹‘𝑥)𝑆(𝐹‘𝑦)}    ⇒   (𝐹:𝐴–1-1→𝐵 → (𝑆 We 𝐵 → 𝑅 We 𝐴))
 
3-Aug-2026nadddird 36945 Natural multiplication distributes over natural addition. Deduction form. (Contributed by Scott Fenton, 3-Aug-2026.)
(𝜑 → 𝐴 ∈ On)    &   (𝜑 → 𝐵 ∈ On)    &   (𝜑 → 𝐶 ∈ On)    ⇒   (𝜑 → ((𝐴 +no 𝐵) ·no 𝐶) = ((𝐴 ·no 𝐶) +no (𝐵 ·no 𝐶)))
 
3-Aug-2026nadddid 36944 Natural multiplication distributes over natural addition. Deduction form. (Contributed by Scott Fenton, 3-Aug-2026.)
(𝜑 → 𝐴 ∈ On)    &   (𝜑 → 𝐵 ∈ On)    &   (𝜑 → 𝐶 ∈ On)    ⇒   (𝜑 → (𝐴 ·no (𝐵 +no 𝐶)) = ((𝐴 ·no 𝐵) +no (𝐴 ·no 𝐶)))
 
3-Aug-2026nadddilem4 36942 Lemma for nadddi 36943. Prove the forward implication. (Contributed by Scott Fenton, 3-Aug-2026.)
(𝜑 → 𝐴 ∈ On)    &   (𝜑 → 𝐵 ∈ On)    &   (𝜑 → 𝐶 ∈ On)    &   (𝜑 → ∀𝑑 ∈ 𝐴 (𝑑 ·no (𝐵 +no 𝐶)) = ((𝑑 ·no 𝐵) +no (𝑑 ·no 𝐶)))    &   (𝜑 → ∀𝑒 ∈ 𝐵 (𝐴 ·no (𝑒 +no 𝐶)) = ((𝐴 ·no 𝑒) +no (𝐴 ·no 𝐶)))    &   (𝜑 → ∀𝑓 ∈ 𝐶 (𝐴 ·no (𝐵 +no 𝑓)) = ((𝐴 ·no 𝐵) +no (𝐴 ·no 𝑓)))    &   (𝜑 → ∀𝑑 ∈ 𝐴 ∀𝑒 ∈ 𝐵 (𝑑 ·no (𝑒 +no 𝐶)) = ((𝑑 ·no 𝑒) +no (𝑑 ·no 𝐶)))    &   (𝜑 → ∀𝑑 ∈ 𝐴 ∀𝑓 ∈ 𝐶 (𝑑 ·no (𝐵 +no 𝑓)) = ((𝑑 ·no 𝐵) +no (𝑑 ·no 𝑓)))    ⇒   (𝜑 → (𝐴 ·no (𝐵 +no 𝐶)) ⊆ ((𝐴 ·no 𝐵) +no (𝐴 ·no 𝐶)))
 
3-Aug-2026nadddilem3 36941 Lemma for nadddi 36943. Prove a subcase of the forward implication. (Contributed by Scott Fenton, 3-Aug-2026.)
(𝜑 → 𝐴 ∈ On)    &   (𝜑 → 𝐵 ∈ On)    &   (𝜑 → 𝐶 ∈ On)    &   (𝜑 → 𝑋 ∈ 𝐴)    &   (𝜑 → 𝑌 ∈ (𝐵 +no 𝐶))    &   (𝜑 → 𝑍 ∈ 𝐵)    &   (𝜑 → 𝑌 ⊆ (𝑍 +no 𝐶))    &   (𝜑 → ∀𝑑 ∈ 𝐴 (𝑑 ·no (𝐵 +no 𝐶)) = ((𝑑 ·no 𝐵) +no (𝑑 ·no 𝐶)))    &   (𝜑 → ∀𝑒 ∈ 𝐵 (𝐴 ·no (𝑒 +no 𝐶)) = ((𝐴 ·no 𝑒) +no (𝐴 ·no 𝐶)))    &   (𝜑 → ∀𝑑 ∈ 𝐴 ∀𝑒 ∈ 𝐵 (𝑑 ·no (𝑒 +no 𝐶)) = ((𝑑 ·no 𝑒) +no (𝑑 ·no 𝐶)))    ⇒   (𝜑 → ((𝑋 ·no (𝐵 +no 𝐶)) +no (𝐴 ·no 𝑌)) ∈ (((𝐴 ·no 𝐵) +no (𝐴 ·no 𝐶)) +no (𝑋 ·no 𝑌)))
 
2-Aug-2026tgaaddcpbl 29334 The angular addition is compatible with angle congruence: by adding congruent angles together, we obtain congruent angles. Theorem 11.22 of [Schwabhauser] p. 99. The angles ⟨“𝑋𝑌𝑆”⟩ and ⟨“𝑆𝑌𝑍”⟩ are added to result in ⟨“𝑋𝑌𝑍”⟩, and ⟨“𝑈𝑉𝑇”⟩ and ⟨“𝑇𝑉𝑊”⟩ are added to result in ⟨“𝑈𝑉𝑊”⟩. (Contributed by Thierry Arnoux, 2-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ (𝑌𝐿𝑆)) ∧ 𝑏 ∈ (𝑃 ∖ (𝑌𝐿𝑆))) ∧ ∃𝑠 ∈ (𝑌𝐿𝑆)𝑠 ∈ (𝑎𝐼𝑏))}    &   𝑄 = {⟨𝑐, 𝑑⟩ ∣ ((𝑐 ∈ (𝑃 ∖ (𝑉𝐿𝑇)) ∧ 𝑑 ∈ (𝑃 ∖ (𝑉𝐿𝑇))) ∧ ∃𝑡 ∈ (𝑉𝐿𝑇)𝑡 ∈ (𝑐𝐼𝑑))}    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑆 ∈ 𝑃)    &   (𝜑 → 𝑇 ∈ 𝑃)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑌 ≠ 𝑆)    &   (𝜑 → 𝑉 ≠ 𝑇)    &   (𝜑 → 𝑋𝑂𝑍)    &   (𝜑 → 𝑈𝑄𝑊)    &   (𝜑 → ⟨“𝑋𝑌𝑆”⟩ ∼ ⟨“𝑈𝑉𝑇”⟩)    &   (𝜑 → ⟨“𝑆𝑌𝑍”⟩ ∼ ⟨“𝑇𝑉𝑊”⟩)    ⇒   (𝜑 → ⟨“𝑋𝑌𝑍”⟩ ∼ ⟨“𝑈𝑉𝑊”⟩)
 
2-Aug-2026tgaaddcpbllem3 29333 Lemma for tgaaddcpbl 29334. (Contributed by Thierry Arnoux, 2-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ (𝑌𝐿𝑆)) ∧ 𝑏 ∈ (𝑃 ∖ (𝑌𝐿𝑆))) ∧ ∃𝑠 ∈ (𝑌𝐿𝑆)𝑠 ∈ (𝑎𝐼𝑏))}    &   𝑄 = {⟨𝑐, 𝑑⟩ ∣ ((𝑐 ∈ (𝑃 ∖ (𝑉𝐿𝑇)) ∧ 𝑑 ∈ (𝑃 ∖ (𝑉𝐿𝑇))) ∧ ∃𝑡 ∈ (𝑉𝐿𝑇)𝑡 ∈ (𝑐𝐼𝑑))}    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑆 ∈ 𝑃)    &   (𝜑 → 𝑇 ∈ 𝑃)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑌 ≠ 𝑆)    &   (𝜑 → 𝑉 ≠ 𝑇)    &   (𝜑 → 𝑋𝑂𝑍)    &   (𝜑 → 𝑈𝑄𝑊)    &   (𝜑 → ⟨“𝑋𝑌𝑆”⟩ ∼ ⟨“𝑈𝑉𝑇”⟩)    &   (𝜑 → ⟨“𝑆𝑌𝑍”⟩ ∼ ⟨“𝑇𝑉𝑊”⟩)    &   (𝜑 → ¬ 𝑌 ∈ (𝑋𝐼𝑍))    ⇒   (𝜑 → ⟨“𝑋𝑌𝑍”⟩ ∼ ⟨“𝑈𝑉𝑊”⟩)
 
2-Aug-2026tgaaddcpbllem2 29332 Lemma for tgaaddcpbl 29334. (Contributed by Thierry Arnoux, 2-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ (𝑌𝐿𝑆)) ∧ 𝑏 ∈ (𝑃 ∖ (𝑌𝐿𝑆))) ∧ ∃𝑠 ∈ (𝑌𝐿𝑆)𝑠 ∈ (𝑎𝐼𝑏))}    &   𝑄 = {⟨𝑐, 𝑑⟩ ∣ ((𝑐 ∈ (𝑃 ∖ (𝑉𝐿𝑇)) ∧ 𝑑 ∈ (𝑃 ∖ (𝑉𝐿𝑇))) ∧ ∃𝑡 ∈ (𝑉𝐿𝑇)𝑡 ∈ (𝑐𝐼𝑑))}    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑆 ∈ 𝑃)    &   (𝜑 → 𝑇 ∈ 𝑃)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑌 ≠ 𝑆)    &   (𝜑 → 𝑉 ≠ 𝑇)    &   (𝜑 → 𝑋𝑂𝑍)    &   (𝜑 → 𝑈𝑄𝑊)    &   (𝜑 → ⟨“𝑋𝑌𝑆”⟩ ∼ ⟨“𝑈𝑉𝑇”⟩)    &   (𝜑 → ⟨“𝑆𝑌𝑍”⟩ ∼ ⟨“𝑇𝑉𝑊”⟩)    &   (𝜑 → ¬ 𝑌 ∈ (𝑋𝐼𝑍))    &   (𝜑 → 𝑅 ∈ (𝑌𝐿𝑆))    &   (𝜑 → 𝑅 ∈ (𝑋𝐼𝑍))    &   (𝜑 → 𝑌 ∈ (𝑆𝐼𝑅))    &   𝑀 = ((pInvG‘𝐺)‘𝑉)    &   𝐾 = (hlG‘𝐺)    ⇒   (𝜑 → ⟨“𝑋𝑌𝑍”⟩ ∼ ⟨“𝑈𝑉𝑊”⟩)
 
2-Aug-2026tgaaddcpbllem1 29331 Lemma for tgaaddcpbl 29334. (Contributed by Thierry Arnoux, 2-Aug-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ (𝑌𝐿𝑆)) ∧ 𝑏 ∈ (𝑃 ∖ (𝑌𝐿𝑆))) ∧ ∃𝑠 ∈ (𝑌𝐿𝑆)𝑠 ∈ (𝑎𝐼𝑏))}    &   𝑄 = {⟨𝑐, 𝑑⟩ ∣ ((𝑐 ∈ (𝑃 ∖ (𝑉𝐿𝑇)) ∧ 𝑑 ∈ (𝑃 ∖ (𝑉𝐿𝑇))) ∧ ∃𝑡 ∈ (𝑉𝐿𝑇)𝑡 ∈ (𝑐𝐼𝑑))}    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑆 ∈ 𝑃)    &   (𝜑 → 𝑇 ∈ 𝑃)    &   (𝜑 → 𝑈 ∈ 𝑃)    &   (𝜑 → 𝑉 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑌 ≠ 𝑆)    &   (𝜑 → 𝑉 ≠ 𝑇)    &   (𝜑 → 𝑋𝑂𝑍)    &   (𝜑 → 𝑈𝑄𝑊)    &   (𝜑 → ⟨“𝑋𝑌𝑆”⟩ ∼ ⟨“𝑈𝑉𝑇”⟩)    &   (𝜑 → ⟨“𝑆𝑌𝑍”⟩ ∼ ⟨“𝑇𝑉𝑊”⟩)    &   (𝜑 → ¬ 𝑌 ∈ (𝑋𝐼𝑍))    &   𝐾 = (hlG‘𝐺)    &   (𝜑 → 𝑅 ∈ (𝑌𝐿𝑆))    &   (𝜑 → 𝑅 ∈ (𝑋𝐼𝑍))    &   (𝜑 → 𝑅(𝐾‘𝑌)𝑆)    ⇒   (𝜑 → ⟨“𝑋𝑌𝑍”⟩ ∼ ⟨“𝑈𝑉𝑊”⟩)
 
1-Aug-20263elfz13 50889 Membership of 3 in the integer interval ( 1 ... 3 ). (Contributed by Jiamin Zhao, 1-Aug-2026.)
3 ∈ (1...3)
 
1-Aug-20262ne3 50886 2 is not equal to 3. (Contributed by Jiamin Zhao, 1-Aug-2026.)
2 ≠ 3
 
1-Aug-20261ne3 50885 1 is not equal to 3. (Contributed by Jiamin Zhao, 1-Aug-2026.)
1 ≠ 3
 
31-Jul-2026crosspval 50898 Value of the cross product of two 3-dimensional real coordinate vectors as a function on (1...3). (Contributed by Jiamin Zhao, 31-Jul-2026.)
((𝐴 ∈ (ℝ ↑m (1...3)) ∧ 𝐵 ∈ (ℝ ↑m (1...3))) → (𝐴⊠𝐵) = (𝑘 ∈ (1...3) ↦ if(𝑘 = 1, (((𝐴‘2) · (𝐵‘3)) − ((𝐴‘3) · (𝐵‘2))), if(𝑘 = 2, (((𝐴‘3) · (𝐵‘1)) − ((𝐴‘1) · (𝐵‘3))), (((𝐴‘1) · (𝐵‘2)) − ((𝐴‘2) · (𝐵‘1)))))))
 
31-Jul-2026df-tripp 50897 Define the scalar triple product of three 3-dimensional real coordinate vectors as the dot product of the first vector 𝑥 with the cross product of the other two (𝑦 and 𝑧). Apply as (𝑦(tripp‘𝑥)𝑧). Vectors are represented as functions on (1...3). (Contributed by Jiamin Zhao, 31-Jul-2026.)
tripp = (𝑥 ∈ (ℝ ↑m (1...3)) ↦ (𝑦 ∈ (ℝ ↑m (1...3)), 𝑧 ∈ (ℝ ↑m (1...3)) ↦ (ℝfld Σg (𝑘 ∈ (1...3) ↦ ((𝑥‘𝑘) · ((𝑦⊠𝑧)‘𝑘))))))
 
31-Jul-2026ctripp 50896 Extend class notation to include the scalar triple product of 3-dimensional real coordinate vectors. (Contributed by Jiamin Zhao, 31-Jul-2026.)
class tripp
 
31-Jul-2026df-crossp 50895 Define the cross product of two 3-dimensional real coordinate vectors. Vectors are represented as functions on (1...3). (Contributed by Jiamin Zhao, 31-Jul-2026.)
⊠ = (𝑢 ∈ (ℝ ↑m (1...3)), 𝑣 ∈ (ℝ ↑m (1...3)) ↦ (𝑘 ∈ (1...3) ↦ if(𝑘 = 1, (((𝑢‘2) · (𝑣‘3)) − ((𝑢‘3) · (𝑣‘2))), if(𝑘 = 2, (((𝑢‘3) · (𝑣‘1)) − ((𝑢‘1) · (𝑣‘3))), (((𝑢‘1) · (𝑣‘2)) − ((𝑢‘2) · (𝑣‘1)))))))
 
31-Jul-2026ccrossp 50894 Extend class notation to include the cross product operation. (Contributed by Jiamin Zhao, 31-Jul-2026.)
class ⊠
 
31-Jul-2026rr3fvcl 50890 The components of a 3-dimensional real coordinate vector are real numbers. (Contributed by Jiamin Zhao, 31-Jul-2026.)
(𝐴 ∈ (ℝ ↑m (1...3)) → ((𝐴‘1) ∈ ℝ ∧ (𝐴‘2) ∈ ℝ ∧ (𝐴‘3) ∈ ℝ))
 
31-Jul-2026numtowerdt 47860 Certain number sets and fields form a tower. In particular, singleton 1, natural numbers, natural numbers with zero, integers, rationals, algebraic reals (notice that current definition allows algebraic numbers to be complex thus the restriction), reals and complex number sets are a tower of proper subsets. (Contributed by Ender Ting, 31-Jul-2026.)
⟨“{1}ℕℕ0ℤℚ(𝔸 ∩ ℝ)ℝℂ”⟩ ∈ ( [⊊] Chain V)
 
31-Jul-2026nadddilem2 36940 Lemma for nadddi 36943. Prove the reverse implication. (Contributed by Scott Fenton, 31-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    &   (𝜑 → 𝐵 ∈ On)    &   (𝜑 → 𝐶 ∈ On)    &   (𝜑 → ∀𝑑 ∈ 𝐴 (𝑑 ·no (𝐵 +no 𝐶)) = ((𝑑 ·no 𝐵) +no (𝑑 ·no 𝐶)))    &   (𝜑 → ∀𝑒 ∈ 𝐵 (𝐴 ·no (𝑒 +no 𝐶)) = ((𝐴 ·no 𝑒) +no (𝐴 ·no 𝐶)))    &   (𝜑 → ∀𝑓 ∈ 𝐶 (𝐴 ·no (𝐵 +no 𝑓)) = ((𝐴 ·no 𝐵) +no (𝐴 ·no 𝑓)))    &   (𝜑 → ∀𝑑 ∈ 𝐴 ∀𝑒 ∈ 𝐵 (𝑑 ·no (𝑒 +no 𝐶)) = ((𝑑 ·no 𝑒) +no (𝑑 ·no 𝐶)))    &   (𝜑 → ∀𝑑 ∈ 𝐴 ∀𝑓 ∈ 𝐶 (𝑑 ·no (𝐵 +no 𝑓)) = ((𝑑 ·no 𝐵) +no (𝑑 ·no 𝑓)))    ⇒   (𝜑 → ((𝐴 ·no 𝐵) +no (𝐴 ·no 𝐶)) ⊆ (𝐴 ·no (𝐵 +no 𝐶)))
 
31-Jul-2026nadddilem1 36939 Lemma for nadddi 36943. Prove a subcase of the reverse implication. (Contributed by Scott Fenton, 31-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    &   (𝜑 → 𝐵 ∈ On)    &   (𝜑 → 𝐶 ∈ On)    &   (𝜑 → ∀𝑑 ∈ 𝐴 (𝑑 ·no (𝐵 +no 𝐶)) = ((𝑑 ·no 𝐵) +no (𝑑 ·no 𝐶)))    &   (𝜑 → ∀𝑓 ∈ 𝐶 (𝐴 ·no (𝐵 +no 𝑓)) = ((𝐴 ·no 𝐵) +no (𝐴 ·no 𝑓)))    &   (𝜑 → ∀𝑑 ∈ 𝐴 ∀𝑓 ∈ 𝐶 (𝑑 ·no (𝐵 +no 𝑓)) = ((𝑑 ·no 𝐵) +no (𝑑 ·no 𝑓)))    ⇒   ((𝜑 ∧ 𝑌 ∈ (𝐴 ·no 𝐶)) → ((𝐴 ·no 𝐵) +no 𝑌) ∈ (𝐴 ·no (𝐵 +no 𝐶)))
 
31-Jul-2026onelssd 36920 An element of an ordinal number is a subset of the number. Deduction form. (Contributed by Scott Fenton, 31-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    &   (𝜑 → 𝐵 ∈ 𝐴)    ⇒   (𝜑 → 𝐵 ⊆ 𝐴)
 
31-Jul-2026ontr2d 36919 Transitive law for ordinal numbers. Exercise 3 of [TakeutiZaring] p. 40. Deduction form. (Contributed by Scott Fenton, 31-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    &   (𝜑 → 𝐶 ∈ On)    &   (𝜑 → 𝐴 ⊆ 𝐵)    &   (𝜑 → 𝐵 ∈ 𝐶)    ⇒   (𝜑 → 𝐴 ∈ 𝐶)
 
31-Jul-2026onelond 36918 An element of an ordinal number is an ordinal number. Theorem 2.2(iii) of [BellMachover] p. 469. Lemma 1.3 of [Schloeder] p. 1. Deduction form. (Contributed by Scott Fenton, 31-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    &   (𝜑 → 𝐵 ∈ 𝐴)    ⇒   (𝜑 → 𝐵 ∈ On)
 
30-Jul-2026nadd32d 36930 Commutative/associative law that swaps the last two terms in a triple sum. Deduction form. (Contributed by Scott Fenton, 30-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    &   (𝜑 → 𝐵 ∈ On)    &   (𝜑 → 𝐶 ∈ On)    ⇒   (𝜑 → ((𝐴 +no 𝐵) +no 𝐶) = ((𝐴 +no 𝐶) +no 𝐵))
 
30-Jul-2026naddassd 36929 Natural addition associates. Deduction form. (Contributed by Scott Fenton, 30-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    &   (𝜑 → 𝐵 ∈ On)    &   (𝜑 → 𝐶 ∈ On)    ⇒   (𝜑 → ((𝐴 +no 𝐵) +no 𝐶) = (𝐴 +no (𝐵 +no 𝐶)))
 
30-Jul-2026naddcomd 36928 Natural addition commutes. Deduction form. (Contributed by Scott Fenton, 30-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    &   (𝜑 → 𝐵 ∈ On)    ⇒   (𝜑 → (𝐴 +no 𝐵) = (𝐵 +no 𝐴))
 
30-Jul-2026naddlidd 36927 Identity law for natural addition. Deduction form. (Contributed by Scott Fenton, 30-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    ⇒   (𝜑 → (∅ +no 𝐴) = 𝐴)
 
30-Jul-2026naddridd 36926 Identity law for natural addition. Deduction form. (Contributed by Scott Fenton, 30-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    ⇒   (𝜑 → (𝐴 +no ∅) = 𝐴)
 
30-Jul-2026nmulcomd 36925 Natural multiplication commutes. Deduction form. (Contributed by Scott Fenton, 30-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    &   (𝜑 → 𝐵 ∈ On)    ⇒   (𝜑 → (𝐴 ·no 𝐵) = (𝐵 ·no 𝐴))
 
30-Jul-2026nmullidd 36924 Identity law for natural multiplication. Deduction form. (Contributed by Scott Fenton, 30-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    ⇒   (𝜑 → (1o ·no 𝐴) = 𝐴)
 
30-Jul-2026nmulridd 36923 Identity law for natural multiplication. Deduction form. (Contributed by Scott Fenton, 30-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    ⇒   (𝜑 → (𝐴 ·no 1o) = 𝐴)
 
30-Jul-2026nmull0d 36922 Natural multiplication by zero. Deduction form. (Contributed by Scott Fenton, 30-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    ⇒   (𝜑 → (∅ ·no 𝐴) = ∅)
 
30-Jul-2026nmulr0d 36921 Natural multiplication by zero. Deduction form. (Contributed by Scott Fenton, 30-Jul-2026.)
(𝜑 → 𝐴 ∈ On)    ⇒   (𝜑 → (𝐴 ·no ∅) = ∅)
 
28-Jul-2026tmachfullfin 47905 Folk theorem. For any algorithm deterministically processing a stream of data (essentially, an infinite tape with cell indices 𝐼 and finite alphabet 𝑈), if it terminates on every possible input, then it never looks beyond a finite portion ∪ ran 𝑆 of the input.

Termination is expressed here with a weaker condition: that an execution may only look at a finite number of cells. Obviously, a program which finishes in a finite number of steps can only scan finite set of cells.

This theorem has many corollaries, such as: any encoding scheme able to represent all integers has at least one non-decodable tape (in other terms, encoding of the infinity).

I no longer have the source for this theorem but I believe I first read about it on LessWrong. My gratitude to Grok for suggesting that this theorem will require Axiom of Choice, and to DeepSeek for suggesting the topology-based proof route. (Contributed by Ender Ting, 28-Jul-2026.)

(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   (𝜑 → ∪ ran 𝑆 ∈ Fin)
 
28-Jul-2026tmachlem-fssscan 47904 Any scan set is finite. (Contributed by Ender Ting, 28-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   (𝜑 → ran 𝑆 ⊆ Fin)
 
28-Jul-2026tmachlem-franscan 47903 There is a finite number of different scan sets. (Contributed by Ender Ting, 28-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   (𝜑 → ran 𝑆 ∈ Fin)
 
28-Jul-2026tmachlem-agreefin 47902 Any agreement set has a finite (singleton) list of possible scans. (Contributed by Ender Ting, 28-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   ((𝜑 ∧ 𝑏 ∈ ran 𝐴) → (𝑆 “ 𝑏) ∈ Fin)
 
28-Jul-2026tmachlem-agreesn 47901 Scans for all tapes of a single agreement set are identical. (Contributed by Ender Ting, 28-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   ((𝜑 ∧ 𝑎 ∈ 𝑇) → (𝑆 “ (𝐴‘𝑎)) = {(𝑆‘𝑎)})
 
28-Jul-2026tmachlem-exagreecover 47900 Particular properties of the finite cover of agreesets. (Contributed by Ender Ting, 28-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   (𝜑 → ∃𝑎(𝑎 ⊆ ran 𝐴 ∧ 𝑎 ∈ Fin ∧ 𝑇 = ∪ 𝑎))
 
28-Jul-2026tmachlem-extpcover 47899 Product topology of tapes admits finite cover. (Contributed by Ender Ting, 28-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   (𝜑 → ∃𝑎 ∈ (𝒫 ran 𝐴 ∩ Fin)∪ (∏t‘(𝑖 ∈ 𝐼 ↦ 𝒫 𝑈)) = ∪ 𝑎)
 
28-Jul-2026tmachlem-exlargecover 47898 Product topology of tapes has an open cover. (Contributed by Ender Ting, 28-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   (𝜑 → ∪ ran 𝐴 = 𝑇)
 
28-Jul-2026tmachlem-uassst 47897 Union of all agreement sets only includes tapes. (Contributed by Ender Ting, 28-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   (𝜑 → ∪ ran 𝐴 ⊆ 𝑇)
 
28-Jul-2026tmachlem-tpbase 47893 The base set of product topology of tapes is the set of tapes. (Contributed by Ender Ting, 28-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   (𝜑 → ∪ (∏t‘(𝑖 ∈ 𝐼 ↦ 𝒫 𝑈)) = 𝑇)
 
27-Jul-2026tmachlem-tpopen2 47896 Variable-renaming lemma connecting tmachlem-agreeprod 47891 and tmachlem-tpopen 47895. (Contributed by Ender Ting, 27-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   ((𝜑 ∧ 𝑎 ∈ 𝑇) → (𝐴‘𝑎) ∈ (∏t‘(𝑏 ∈ 𝐼 ↦ 𝒫 𝑈)))
 
27-Jul-2026tmachlem-tpopen 47895 Agreement sets are open in the product topology of tapes. (Contributed by Ender Ting, 27-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   ((𝜑 ∧ 𝑎 ∈ 𝑇) → X𝑏 ∈ 𝐼 if(𝑏 ∈ (𝑆‘𝑎), {(𝑎‘𝑏)}, 𝑈) ∈ (∏t‘(𝑖 ∈ 𝐼 ↦ 𝒫 𝑈)))
 
27-Jul-2026tmachlem-tpitem 47894 Topology lemma. (Contributed by Ender Ting, 27-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   ((𝜑 ∧ 𝑎 ∈ 𝐼) → ((𝑖 ∈ 𝐼 ↦ 𝒫 𝑈)‘𝑎) = 𝒫 𝑈)
 
27-Jul-2026tmachlem-tpcomp 47892 Product (discrete) topology of tapes is compact by Tychonoff's theorem. To work for infinite index sets (such as ℤ for 𝐼 which is the main interpretation), it requires Choice. (Contributed by Ender Ting, 27-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   (𝜑 → (∏t‘(𝑖 ∈ 𝐼 ↦ 𝒫 𝑈)) ∈ Comp)
 
27-Jul-2026tmachlem-agreeprod 47891 Agreement set can be written as infinite product of acceptable values for tape's cells. (Contributed by Ender Ting, 27-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   ((𝜑 ∧ 𝑎 ∈ 𝑇) → (𝐴‘𝑎) = X𝑖 ∈ 𝐼 if(𝑖 ∈ (𝑆‘𝑎), {(𝑎‘𝑖)}, 𝑈))
 
27-Jul-2026tmachlem-agreeself 47890 Any tape belongs to its own agreement set. (Contributed by Ender Ting, 27-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   ((𝜑 ∧ 𝑎 ∈ 𝑇) → 𝑎 ∈ (𝐴‘𝑎))
 
27-Jul-2026tmachlem-finscan 47889 Execution on any tape only scanned a finite number of cells. (Contributed by Ender Ting, 27-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   ((𝜑 ∧ 𝑎 ∈ 𝑇) → (𝑆‘𝑎) ∈ Fin)
 
27-Jul-2026tmachlem-extapes 47888 The class of all tapes is a set. (Contributed by Ender Ting, 27-Jul-2026.)
(𝜑 → 𝑈 ∈ Fin)    &   (𝜑 → 𝐼 ∈ V)    &   (𝜑 → 𝑇 = (𝑈 ↑m 𝐼))    &   (𝜑 → 𝑆:𝑇⟶(𝒫 𝐼 ∩ Fin))    &   (𝜑 → 𝐴 = (𝑧 ∈ 𝑇 ↦ {𝑦 ∈ 𝑇 ∣ (𝑦 ↾ (𝑆‘𝑧)) = (𝑧 ↾ (𝑆‘𝑧))}))    &   (𝜑 → ∀𝑧 ∈ 𝑇 ∀𝑦 ∈ (𝐴‘𝑧)(𝑆‘𝑦) = (𝑆‘𝑧))    ⇒   (𝜑 → 𝑇 ∈ V)
 
27-Jul-2026nadddi 36943 Natural multiplication distributes over natural addition. (Contributed by Scott Fenton, 27-Jul-2026.)
((𝐴 ∈ On ∧ 𝐵 ∈ On ∧ 𝐶 ∈ On) → (𝐴 ·no (𝐵 +no 𝐶)) = ((𝐴 ·no 𝐵) +no (𝐴 ·no 𝐶)))
 
24-Jul-2026goldratval 47880 Value of the golden ratio. (Contributed by Ender Ting, 24-Jul-2026.)
𝐹 = (2 · (cos‘(π / 5)))    ⇒   𝐹 = ((1 + (√‘5)) / 2)
 
24-Jul-2026goldratmolem4 47879 Lemma 4 for determining the value of golden ratio. (Contributed by Ender Ting, 24-Jul-2026.)
𝐹 = (2 · (cos‘(π / 5)))    ⇒   (((𝐹↑2) − 𝐹) − 1) = 0
 
24-Jul-2026goldpolyfactor 47871 Factorization of a polynomial which has golden ratio among its roots, done by term-by-term-by-term multiplying and summing a few shorter polynomials. (Contributed by Ender Ting, 24-Jul-2026.)
𝐹 ∈ ℂ    ⇒   (((((𝐹↑2) − 𝐹) − 1) · (((𝐹↑2) − 𝐹) − 1)) · (𝐹 + 2)) = ((((𝐹↑5) − (5 · (𝐹↑3))) + (5 · 𝐹)) + 2)
 
24-Jul-2026chnrun2 47854 Superadditivity of chain constructor over relation parameter. (Contributed by Ender Ting, 24-Jul-2026.)
((𝑅 Chain 𝐵) ∪ ( < Chain 𝐵)) ⊆ ((𝑅 ∪ < ) Chain 𝐵)
 
24-Jul-2026chnrun 47853 Satisfying either of two chain relations is sufficient to make a chain under their union. (Contributed by Ender Ting, 24-Jul-2026.)
((𝐴 ∈ (𝑅 Chain 𝐵) ∨ 𝐴 ∈ ( < Chain 𝐵)) → 𝐴 ∈ ((𝑅 ∪ < ) Chain 𝐵))
 
24-Jul-2026chnrin2 47852 Distribution of chain class constructor over relation intersection. (Contributed by Ender Ting, 24-Jul-2026.)
((𝑅 ∩ < ) Chain 𝐵) = ((𝑅 Chain 𝐵) ∩ ( < Chain 𝐵))
 
24-Jul-2026chnrrin 47851 A chain of elements satisfying two relations at once is a chain under either of them. (Contributed by Ender Ting, 24-Jul-2026.)
(𝐴 ∈ ((𝑅 ∩ < ) Chain 𝐵) → (𝐴 ∈ (𝑅 Chain 𝐵) ∧ 𝐴 ∈ ( < Chain 𝐵)))
 
24-Jul-2026chnrin 47850 Satisfying two chain relations makes a chain under their intersection. (Contributed by Ender Ting, 24-Jul-2026.)
((𝐴 ∈ (𝑅 Chain 𝐵) ∧ 𝐴 ∈ ( < Chain 𝐵)) → 𝐴 ∈ ((𝑅 ∩ < ) Chain 𝐵))
 
24-Jul-2026chndun2 47849 Superaddivity of chain constructor over alphabet parameter. (Contributed by Ender Ting, 24-Jul-2026.)
((𝑅 Chain 𝐵) ∪ (𝑅 Chain 𝐶)) ⊆ (𝑅 Chain (𝐵 ∪ 𝐶))
 
24-Jul-2026chndun 47848 Chains in either of two alphabets are chains in their union. (Contributed by Ender Ting, 24-Jul-2026.)
((𝐴 ∈ (𝑅 Chain 𝐵) ∨ 𝐴 ∈ (𝑅 Chain 𝐶)) → 𝐴 ∈ (𝑅 Chain (𝐵 ∪ 𝐶)))
 
24-Jul-2026chndin2 47847 Distribution of chain class constructor over alphabet intersection. (Contributed by Ender Ting, 24-Jul-2026.)
(𝑅 Chain (𝐵 ∩ 𝐶)) = ((𝑅 Chain 𝐵) ∩ (𝑅 Chain 𝐶))
 
24-Jul-2026chndrin 47846 A chain whose alphabet is intersection of two classes is also a chain in each of those alphabets. (Contributed by Ender Ting, 24-Jul-2026.)
(𝐴 ∈ (𝑅 Chain (𝐵 ∩ 𝐶)) → (𝐴 ∈ (𝑅 Chain 𝐵) ∧ 𝐴 ∈ (𝑅 Chain 𝐶)))
 
24-Jul-2026chndin 47845 A chain in two alphabets at once is also a chain in their intersection. (Contributed by Ender Ting, 24-Jul-2026.)
((𝐴 ∈ (𝑅 Chain 𝐵) ∧ 𝐴 ∈ (𝑅 Chain 𝐶)) → 𝐴 ∈ (𝑅 Chain (𝐵 ∩ 𝐶)))
 
24-Jul-2026wrddun2 47844 Superadditivity of word constructor. Class of words over union alphabet includes all words over either alphabet in the union; if 𝐵 and 𝐶 are non-empty and different, then this subclass relation is strict because of the words which have symbols both from 𝐵 and from 𝐶. (Contributed by Ender Ting, 24-Jul-2026.)
(Word 𝐵 ∪ Word 𝐶) ⊆ Word (𝐵 ∪ 𝐶)
 
24-Jul-2026wrddun 47843 Words in either of two alphabets are words in their union. (Contributed by Ender Ting, 24-Jul-2026.)
((𝐴 ∈ Word 𝐵 ∨ 𝐴 ∈ Word 𝐶) → 𝐴 ∈ Word (𝐵 ∪ 𝐶))
 
24-Jul-2026wrddin2 47842 Distribution of word class constructor over class intersection. (Contributed by Ender Ting, 24-Jul-2026.)
Word (𝐵 ∩ 𝐶) = (Word 𝐵 ∩ Word 𝐶)
 
24-Jul-2026wrddrin 47841 A word whose alphabet is intersection of two classes is also a word in each of those alphabets. (Contributed by Ender Ting, 24-Jul-2026.)
(𝐴 ∈ Word (𝐵 ∩ 𝐶) → (𝐴 ∈ Word 𝐵 ∧ 𝐴 ∈ Word 𝐶))
 
24-Jul-2026wrddin 47840 A word in two alphabets is also a word under their intersection. (Contributed by Ender Ting, 24-Jul-2026.)
((𝐴 ∈ Word 𝐵 ∧ 𝐴 ∈ Word 𝐶) → 𝐴 ∈ Word (𝐵 ∩ 𝐶))
 
24-Jul-2026ricer 20736 Ring isomorphism is an equivalence relation. (Contributed by Jeff Madsen, 16-Jun-2011.) (Revised by Mario Carneiro, 12-Aug-2015.) (Revised by AV, 24-Jul-2026.)
≃𝑟 Er Ring
 
24-Jul-2026ricref 20728 Ring isomorphism is reflexive. (Contributed by by AV, 24-Jul-2026.)
(𝑅 ∈ Ring → 𝑅 ≃𝑟 𝑅)
 
24-Jul-2026ricrel 20724 The domain of the ring isomorphism relation is a relation. (Contributed by AV, 24-Jul-2026.)
Rel ≃𝑟
 
24-Jul-2026rhmkerinj 20720 A ring homomorphism is injective if and only if its kernel is zero. (Contributed by Jeff Madsen, 16-Jun-2011.) (Revised by AV, 24-Jul-2026.)
𝐵 = (Base‘𝑅)    &   𝐶 = (Base‘𝑆)    &    0 = (0g‘𝑅)    &   𝑍 = (0g‘𝑆)    ⇒   (𝐹 ∈ (𝑅 RingHom 𝑆) → (𝐹:𝐵–1-1→𝐶 ↔ (◡𝐹 “ {𝑍}) = { 0 }))
 
24-Jul-2026rimval 20710 The set of ring isomorphisms. (Contributed by Jeff Madsen, 16-Jun-2011.) (Revised by AV, 24-Jul-2026.)
𝐵 = (Base‘𝑅)    &   𝐶 = (Base‘𝑆)    ⇒   (𝑅 RingIso 𝑆) = {𝑓 ∈ (𝑅 RingHom 𝑆) ∣ 𝑓:𝐵–1-1-onto→𝐶}
 
24-Jul-2026isrhm0 20686 The predicate "is a ring homomorphism from 𝑅 to 𝑆". (Contributed by Jeff Madsen, 19-Jun-2010.) (Revised by AV, 24-Jul-2026.)
𝐵 = (Base‘𝑅)    &   𝐶 = (Base‘𝑆)    &    1 = (1r‘𝑅)    &   𝑁 = (1r‘𝑆)    &    · = (.r‘𝑅)    &    × = (.r‘𝑆)    &    + = (+g‘𝑅)    &    ⨣ = (+g‘𝑆)    ⇒   ((𝑅 ∈ Ring ∧ 𝑆 ∈ Ring) → (𝐹 ∈ (𝑅 RingHom 𝑆) ↔ (𝐹:𝐵⟶𝐶 ∧ (𝐹‘ 1 ) = 𝑁 ∧ ∀𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐵 ((𝐹‘(𝑥 + 𝑦)) = ((𝐹‘𝑥) ⨣ (𝐹‘𝑦)) ∧ (𝐹‘(𝑥 · 𝑦)) = ((𝐹‘𝑥) × (𝐹‘𝑦))))))
 
24-Jul-2026rhmval0 20685 The set of ring homomorphisms. (Contributed by Jeff Madsen, 19-Jun-2010.) (Revised by Mario Carneiro, 22-Sep-2015.) (Revised by AV, 24-Jul-2026.)
𝐵 = (Base‘𝑅)    &   𝐶 = (Base‘𝑆)    &    1 = (1r‘𝑅)    &   𝑁 = (1r‘𝑆)    &    · = (.r‘𝑅)    &    × = (.r‘𝑆)    &    + = (+g‘𝑅)    &    ⨣ = (+g‘𝑆)    ⇒   ((𝑅 ∈ Ring ∧ 𝑆 ∈ Ring) → (𝑅 RingHom 𝑆) = {𝑓 ∈ (𝐶 ↑m 𝐵) ∣ ((𝑓‘ 1 ) = 𝑁 ∧ ∀𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐵 ((𝑓‘(𝑥 + 𝑦)) = ((𝑓‘𝑥) ⨣ (𝑓‘𝑦)) ∧ (𝑓‘(𝑥 · 𝑦)) = ((𝑓‘𝑥) × (𝑓‘𝑦))))})
 
23-Jul-2026goldratmolem3 47878 Lemma 3 for determining the value of golden ratio. (Contributed by Ender Ting, 23-Jul-2026.)
𝐹 = (2 · (cos‘(π / 5)))    ⇒   ((((𝐹↑5) − (5 · (𝐹↑3))) + (5 · 𝐹)) + 2) = 0
 
23-Jul-2026isdrng5 20988 A division ring is a ring in which 1 ≠ 0 and every nonzero element is invertible. (Contributed by Jeff Madsen, 8-Jun-2010.) (Revised by AV, 23-Jul-2026.)
𝐵 = (Base‘𝑅)    &    0 = (0g‘𝑅)    &    1 = (1r‘𝑅)    &    · = (.r‘𝑅)    ⇒   (𝑅 ∈ DivRing ↔ (𝑅 ∈ Ring ∧ 1 ≠ 0 ∧ ∀𝑥 ∈ (𝐵 ∖ { 0 })∃𝑦 ∈ 𝐵 (𝑦 · 𝑥) = 1 ))
 
23-Jul-2026brric2 20734 The ring isomorphism relation. (Contributed by Jeff Madsen, 16-Jun-2011.) (Revised by AV, 23-Jul-2026.)
((𝑅 ∈ Ring ∧ 𝑆 ∈ Ring) → (𝑅 ≃𝑟 𝑆 ↔ ∃𝑓 𝑓 ∈ (𝑅 RingIso 𝑆)))
 
23-Jul-2026ricrcl 20730 Ring isomorphism implies the right side is a ring. (Contributed by AV, 23-Jul-2026.)
(𝑅 ≃𝑟 𝑆 → 𝑆 ∈ Ring)
 
23-Jul-2026riclcl 20729 Ring isomorphism implies the left side is a ring. (Contributed by AV, 23-Jul-2026.)
(𝑅 ≃𝑟 𝑆 → 𝑅 ∈ Ring)
 
23-Jul-2026rhm0 20703 A ring homomorphism preserves 0. (Contributed by Jeff Madsen, 2-Jan-2011.) (Revised by AV, 23-Jul-2026.)
0 = (0g‘𝑅)    &   𝑍 = (0g‘𝑆)    ⇒   (𝐹 ∈ (𝑅 RingHom 𝑆) → (𝐹‘ 0 ) = 𝑍)
 
22-Jul-2026sqrtnpoly 47887 Square root function is not polynomial with complex coefficients either. Otherwise, its composition with a square monomial - the identity - would have to be of even degree. (Contributed by Ender Ting, 22-Jul-2026.)
¬ √ ∈ (Poly‘ℂ)
 
22-Jul-2026sqrtrrnpoly 47886 Real square root is not a polynomial with real coefficients, because its value is imaginary for negative arguments. (Contributed by Ender Ting, 22-Jul-2026.)
¬ √ ∈ (Poly‘ℝ)
 
22-Jul-2026sqrtqaa 47859 Square root of a rational number is algebraic. (Contributed by Ender Ting, 22-Jul-2026.)
(𝐴 ∈ ℚ → (√‘𝐴) ∈ 𝔸)
 
22-Jul-2026sqrtnzqaa 47858 Square root of a nonzero rational is algebraic. (Contributed by Ender Ting, 22-Jul-2026.)
((𝐴 ∈ ℚ ∧ 𝐴 ≠ 0) → (√‘𝐴) ∈ 𝔸)
 
22-Jul-2026zrdrng 21006 A zero ring is not a division ring. (Contributed by FL, 24-Jan-2010.) (Revised by AV, 22-Jul-2026.)
0 = (0g‘𝑅)    &    1 = (1r‘𝑅)    ⇒   ( 0 = 1 → ¬ 𝑅 ∈ DivRing)
 
22-Jul-2026isdrng3 20987 A division ring is a ring in which 1 ≠ 0 and every nonzero element is invertible. (Contributed by Jeff Madsen, 8-Jun-2010.) (Revised by AV, 22-Jul-2026.)
𝐵 = (Base‘𝑅)    &    0 = (0g‘𝑅)    &    1 = (1r‘𝑅)    &    · = (.r‘𝑅)    ⇒   (𝑅 ∈ DivRing ↔ (𝑅 ∈ Ring ∧ 1 ≠ 0 ∧ ∀𝑥 ∈ (𝐵 ∖ { 0 })∃𝑦 ∈ (𝐵 ∖ { 0 })(𝑦 · 𝑥) = 1 ))
 
22-Jul-2026isdrng3lem2 20986 Lemma for isdrng3 20987 (for the right to left implication). Formerly part of proof for isdrng3 20987. (Contributed by Jeff Madsen, 8-Jun-2010.) (Revised by AV, 22-Jul-2026.)
𝐵 = (Base‘𝑅)    &    0 = (0g‘𝑅)    &    1 = (1r‘𝑅)    &    · = (.r‘𝑅)    ⇒   ((𝑅 ∈ Ring ∧ 1 ≠ 0 ∧ ∀𝑥 ∈ (𝐵 ∖ { 0 })∃𝑦 ∈ (𝐵 ∖ { 0 })(𝑦 · 𝑥) = 1 ) → ((mulGrp‘𝑅) ↾s (𝐵 ∖ { 0 })) ∈ Grp)
 
22-Jul-2026isdrng3lem1 20985 Lemma for isdrng3 20987 (for the left to right implication). Formerly part of proof for isdrng3 20987. (Contributed by Jeff Madsen, 8-Jun-2010.) (Revised by AV, 22-Jul-2026.)
𝐵 = (Base‘𝑅)    &    0 = (0g‘𝑅)    &    1 = (1r‘𝑅)    &    · = (.r‘𝑅)    ⇒   ((𝑅 ∈ Ring ∧ ((mulGrp‘𝑅) ↾s (𝐵 ∖ { 0 })) ∈ Grp) → ∀𝑥 ∈ (𝐵 ∖ { 0 })∃𝑦 ∈ (𝐵 ∖ { 0 })(𝑦 · 𝑥) = 1 )
 
22-Jul-2026isdrng3lem0 20984 Lemma for isdrng3 20987: The base set of a multipication group restricted to a subset of the original base set. (Contributed by AV, 22-Jul-2026.)
𝐵 = (Base‘𝑅)    ⇒   (Base‘((mulGrp‘𝑅) ↾s (𝐵 ∖ 𝑋))) = (𝐵 ∖ 𝑋)
 
22-Jul-2026hta 9943 A ZFC emulation of Hilbert's transfinite axiom. The set 𝐵 has the properties of Hilbert's epsilon, except that it also depends on a well-ordering 𝑅. This theorem arose from discussions with Raph Levien on 5-Mar-2004 about translating the HOL proof language, which uses Hilbert's epsilon. See https://us.metamath.org/downloads/choice.txt (copy of obsolete link http://ghilbert.org/choice.txt) and https://us.metamath.org/downloads/megillaward2005he.pdf.

Hilbert's epsilon is described at http://plato.stanford.edu/entries/epsilon-calculus/. This theorem differs from Hilbert's transfinite axiom described on that page in that it requires 𝑅 We 𝐴 as an antecedent. Class 𝐴 collects the sets of the least rank for which 𝜑(𝑥) is true. Class 𝐵, which emulates Hilbert's epsilon, is the minimum element in a well-ordering 𝑅 on 𝐴.

If a well-ordering 𝑅 on 𝐴 can be expressed in a closed form, as might be the case if we are working with say natural numbers, we can eliminate the antecedent with modus ponens, giving us the exact equivalent of Hilbert's transfinite axiom. Otherwise, we replace 𝑅 with a dummy setvar variable, say 𝑤, and attach 𝑤 We 𝐴 as an antecedent in each step of the ZFC version of the HOL proof until the epsilon is eliminated. At that point, 𝐵 (which will have 𝑤 as a free variable) will no longer be present, and we can eliminate 𝑤 We 𝐴 by applying exlimiv 1963 and weth 10554, using scottex 9914 to establish the existence of 𝐴.

For a version of this theorem scheme using class (meta)variables instead of wff (meta)variables, see htalem 9942. (Contributed by NM, 11-Mar-2004.) (Revised by Mario Carneiro, 25-Jun-2015.) Use the Scott operation. (Revised by BTernaryTau, 22-Jul-2026.)

𝐴 = Scott {𝑥 ∣ 𝜑}    &   𝐵 = (℩𝑦 ∈ 𝐴 ∀𝑧 ∈ 𝐴 ¬ 𝑧𝑅𝑦)    ⇒   (𝑅 We 𝐴 → (𝜑 → [𝐵 / 𝑥]𝜑))
 
22-Jul-2026scott0bs 9925 Theorem scheme version of scott0b 9918. The collection of all 𝑥 of minimum rank such that 𝜑(𝑥) is true, is not empty iff there is an 𝑥 such that 𝜑(𝑥) holds. (Contributed by NM, 13-Oct-2003.) Use the Scott operation. (Revised by BTernaryTau, 22-Jul-2026.)
(∃𝑥𝜑 ↔ Scott {𝑥 ∣ 𝜑} ≠ ∅)
 
21-Jul-2026alseu-no-surprise 50878 Demonstrate that there is never a "surprise" when using the "all some one" quantifier, that is, it is never possible for the consequent to be both always true and always false. This follows from als-no-surprise 50846 by alseuals 50864. For a contrast, see alimp-surprise 50820. (Contributed by David A. Wheeler, 21-Jul-2026.)
¬ (∀∃!𝑥(𝜑 → 𝜓) ∧ ∀∃!𝑥(𝜑 → ¬ 𝜓))
 
21-Jul-2026alseueu 50877 "The 𝜑 is 𝜓 " implies that exactly one thing is both 𝜑 and 𝜓. This is the half of dfalseu2 50876 that drops the universal conjunct; it does not reverse, so ∃!𝑥(𝜑 ∧ 𝜓) cannot be used in place of an "all some one" statement. (Contributed by David A. Wheeler, 21-Jul-2026.)
(∀∃!𝑥(𝜑 → 𝜓) → ∃!𝑥(𝜑 ∧ 𝜓))
 
21-Jul-2026dfalseu2 50876 An "all some one" statement is equivalent to its universal part conjoined with the claim that exactly one 𝑥 satisfies both 𝜑 and 𝜓. In other words, given ∀𝑥(𝜑 → 𝜓), requiring exactly one 𝑥 to satisfy 𝜑, which is what df-alseu 50861 requires, and requiring exactly one 𝑥 to satisfy (𝜑 ∧ 𝜓) come to the same thing. Read 𝜑 as "is a king" and 𝜓 as "is hungry": if every king is hungry, then "there is exactly one king" and "there is exactly one hungry king" say the same thing, so either of them, together with "every king is hungry", gives "the king is hungry".

The universal conjunct is what makes that work, and it cannot be dropped. ∃!𝑥(𝜑 ∧ 𝜓) on its own is strictly weaker than ∀∃!𝑥(𝜑 → 𝜓), since it is satisfied when many things are 𝜑 and just one of those is 𝜓, as in a region with five kings exactly one of whom is hungry; see alseueu 50877 for the one direction that does hold without it. Uniqueness attaches to the antecedent, not to the conjunction. Russell's analysis of a definite description is built the same way: its uniqueness clause constrains the description predicate alone, while the predication is a separate conjunct. See his worked example of "the father of Charles II was executed", [Russell1905] p. 482. (Contributed by David A. Wheeler, 21-Jul-2026.)

(∀∃!𝑥(𝜑 → 𝜓) ↔ (∀𝑥(𝜑 → 𝜓) ∧ ∃!𝑥(𝜑 ∧ 𝜓)))
 
21-Jul-2026nfralseu 50875 Bound-variable hypothesis builder for "all some one" restricted to a class. This is the "all some one" counterpart of nfrals 50844. (Contributed by David A. Wheeler, 21-Jul-2026.)
Ⅎ𝑥𝐴    &   Ⅎ𝑥𝜑    &   Ⅎ𝑥𝜓    ⇒   Ⅎ𝑥∀∃!𝑦 ∈ 𝐴(𝜑 → 𝜓)
 
21-Jul-2026nfalseu 50874 Bound-variable hypothesis builder for "all some one". This is the "all some one" counterpart of nfals 50843. Unlike nfals 50843 it requires 𝑥 and 𝑦 to be disjoint, because the corresponding builder for ∃! is nfeuw 2619, which requires it; the version without that requirement, nfeu 2620, depends on ax-13 2402 and its use is discouraged. (Contributed by David A. Wheeler, 21-Jul-2026.)
Ⅎ𝑥𝜑    &   Ⅎ𝑥𝜓    ⇒   Ⅎ𝑥∀∃!𝑦(𝜑 → 𝜓)
 
21-Jul-2026ralseubii 50873 Congruence for "all some one" restricted to a class. This is the "all some one" counterpart of ralsbii 50841. (Contributed by David A. Wheeler, 21-Jul-2026.)
(𝜑 ↔ 𝜒)    &   (𝜓 ↔ 𝜃)    ⇒   (∀∃!𝑥 ∈ 𝐴(𝜑 → 𝜓) ↔ ∀∃!𝑥 ∈ 𝐴(𝜒 → 𝜃))
 
21-Jul-2026alseubii 50872 Congruence: equivalents may be substituted inside an "all some one". This is the "all some one" counterpart of alsbii 50840. (Contributed by David A. Wheeler, 21-Jul-2026.)
(𝜑 ↔ 𝜒)    &   (𝜓 ↔ 𝜃)    ⇒   (∀∃!𝑥(𝜑 → 𝜓) ↔ ∀∃!𝑥(𝜒 → 𝜃))
 
21-Jul-2026ralseu2d 50871 Deduction rule: Given "all some one" applied to a class, you can extract the "exactly one" part. Note that the witness must satisfy the antecedent 𝜓, not merely be a member of 𝐴. (Contributed by David A. Wheeler, 21-Jul-2026.)
(𝜑 → ∀∃!𝑥 ∈ 𝐴(𝜓 → 𝜒))    ⇒   (𝜑 → ∃!𝑥 ∈ 𝐴 𝜓)
 
21-Jul-2026ralseu1d 50870 Deduction rule: Given "all some one" applied to a class, you can extract the "for all" part. (Contributed by David A. Wheeler, 21-Jul-2026.)
(𝜑 → ∀∃!𝑥 ∈ 𝐴(𝜓 → 𝜒))    ⇒   (𝜑 → ∀𝑥 ∈ 𝐴 (𝜓 → 𝜒))
 
21-Jul-2026alseu2d 50869 Deduction rule: Given "all some one" applied to a top-level inference, you can extract the "exactly one" part. (Contributed by David A. Wheeler, 21-Jul-2026.)
(𝜑 → ∀∃!𝑥(𝜓 → 𝜒))    ⇒   (𝜑 → ∃!𝑥𝜓)
 
21-Jul-2026alseu1d 50868 Deduction rule: Given "all some one" applied to a top-level inference, you can extract the "for all" part. (Contributed by David A. Wheeler, 21-Jul-2026.)
(𝜑 → ∀∃!𝑥(𝜓 → 𝜒))    ⇒   (𝜑 → ∀𝑥(𝜓 → 𝜒))
 
21-Jul-2026ralseud 50867 Introduction rule for "all some one" restricted to a class. This is the converse of ralseu1d 50870 and ralseu2d 50871 taken together. (Contributed by David A. Wheeler, 21-Jul-2026.)
(𝜑 → ∀𝑥 ∈ 𝐴 (𝜓 → 𝜒))    &   (𝜑 → ∃!𝑥 ∈ 𝐴 𝜓)    ⇒   (𝜑 → ∀∃!𝑥 ∈ 𝐴(𝜓 → 𝜒))
 
21-Jul-2026alseud 50866 Introduction rule: "all some one" holds if the "for all" part holds and the antecedent has exactly one witness. This is the converse of alseu1d 50868 and alseu2d 50869 taken together. (Contributed by David A. Wheeler, 21-Jul-2026.)
(𝜑 → ∀𝑥(𝜓 → 𝜒))    &   (𝜑 → ∃!𝑥𝜓)    ⇒   (𝜑 → ∀∃!𝑥(𝜓 → 𝜒))
 
21-Jul-2026ralseurals 50865 "All some one" restricted to a class implies "all some" restricted to that class. Restricted counterpart of alseuals 50864. (Contributed by David A. Wheeler, 21-Jul-2026.)
(∀∃!𝑥 ∈ 𝐴(𝜑 → 𝜓) → ∀∃𝑥 ∈ 𝐴(𝜑 → 𝜓))
 
21-Jul-2026alseuals 50864 "All some one" implies "all some": requiring exactly one witness is stronger than requiring at least one. Any consequence of an allsome statement is therefore a consequence of the corresponding "all some one" statement, which is how alseu-no-surprise 50878 is proved. (Contributed by David A. Wheeler, 21-Jul-2026.)
(∀∃!𝑥(𝜑 → 𝜓) → ∀∃𝑥(𝜑 → 𝜓))
 
21-Jul-2026dfralseu2 50863 The bounded "all some one" form is the general form with the class membership folded into the antecedent. This is the "all some one" counterpart of dfrals2 50830. (Contributed by David A. Wheeler, 21-Jul-2026.)
(∀∃!𝑥 ∈ 𝐴(𝜑 → 𝜓) ↔ ∀∃!𝑥((𝑥 ∈ 𝐴 ∧ 𝜑) → 𝜓))
 
21-Jul-2026df-ralseu 50862 Define "all some one" applied to a class, which means 𝜓 is true whenever 𝜑 is true for 𝑥 in 𝐴, and exactly one 𝑥 in 𝐴 satisfies 𝜑. (Contributed by David A. Wheeler, 21-Jul-2026.)
(∀∃!𝑥 ∈ 𝐴(𝜑 → 𝜓) ↔ (∀𝑥 ∈ 𝐴 (𝜑 → 𝜓) ∧ ∃!𝑥 ∈ 𝐴 𝜑))
 
21-Jul-2026df-alseu 50861 Define "all some one" applied to a top-level implication, which means 𝜓 is true whenever 𝜑 is true and exactly one 𝑥 satisfies 𝜑. (Contributed by David A. Wheeler, 21-Jul-2026.)
(∀∃!𝑥(𝜑 → 𝜓) ↔ (∀𝑥(𝜑 → 𝜓) ∧ ∃!𝑥𝜑))
 
21-Jul-2026wralseu 50860 Extend wff definition to include "all some one" applied to a class, which means 𝜓 is true whenever 𝜑 is true for 𝑥 in 𝐴, and exactly one 𝑥 in 𝐴 satisfies 𝜑. (Contributed by David A. Wheeler, 21-Jul-2026.)
wff ∀∃!𝑥 ∈ 𝐴(𝜑 → 𝜓)
 
21-Jul-2026walseu 50859 Extend wff definition to include "all some one" applied to a top-level implication, which means 𝜓 is true whenever 𝜑 is true, and exactly one 𝑥 satisfies 𝜑. (Contributed by David A. Wheeler, 21-Jul-2026.)
wff ∀∃!𝑥(𝜑 → 𝜓)
 
21-Jul-2026sqrtnnaa 47857 Square root of a natural number is algebraic. (Contributed by Ender Ting, 21-Jul-2026.)
(𝐴 ∈ ℕ → (√‘𝐴) ∈ 𝔸)
 
21-Jul-2026naddle 36938 Condition for bounding natural addition above. (Contributed by Scott Fenton, 21-Jul-2026.)
((𝐴 ∈ On ∧ 𝐵 ∈ On ∧ 𝐶 ∈ On) → ((𝐴 +no 𝐵) ⊆ 𝐶 ↔ (∀𝑎 ∈ 𝐴 (𝑎 +no 𝐵) ∈ 𝐶 ∧ ∀𝑏 ∈ 𝐵 (𝐴 +no 𝑏) ∈ 𝐶)))
 
21-Jul-2026ltnadd 36937 Condition for bounding a natural sum below. (Contributed by Scott Fenton, 21-Jul-2026.)
((𝐴 ∈ On ∧ 𝐵 ∈ On ∧ 𝐶 ∈ On) → (𝐴 ∈ (𝐵 +no 𝐶) ↔ (∃𝑏 ∈ 𝐵 𝐴 ⊆ (𝑏 +no 𝐶) ∨ ∃𝑐 ∈ 𝐶 𝐴 ⊆ (𝐵 +no 𝑐))))
 
21-Jul-2026nmullid 36917 Identity law for natural multiplication. (Contributed by Scott Fenton, 21-Jul-2026.)
(𝐴 ∈ On → (1o ·no 𝐴) = 𝐴)
 
21-Jul-2026nmulrid 36916 Identity law for natural multiplication. (Contributed by Scott Fenton, 21-Jul-2026.)
(𝐴 ∈ On → (𝐴 ·no 1o) = 𝐴)
 
21-Jul-2026aaliou3r 26661 The sum presented above is convergent, which means that the "Liouville number" is indeed real. (Contributed by Ender Ting, 21-Jul-2026.)
Σ𝑘 ∈ ℕ (2↑-(!‘𝑘)) ∈ ℝ
 
21-Jul-20261aa 26632 One is algebraic. (Contributed by Ender Ting, 21-Jul-2026.)
1 ∈ 𝔸
 
21-Jul-20260aa 26631 Zero is algebraic. (Contributed by Ender Ting, 21-Jul-2026.)
0 ∈ 𝔸
 
20-Jul-2026ralsanmo 50851 An "all some" statement restricted to a class, conjoined with the claim that at most one 𝑥 in 𝐴 satisfies its antecedent, is equivalent to the universal part conjoined with the claim that exactly one 𝑥 in 𝐴 satisfies the antecedent. This is the restricted counterpart of alsanmo 50850. (Contributed by Peter Mazsa and David A. Wheeler, 20-Jul-2026.)
((∀∃𝑥 ∈ 𝐴(𝜑 → 𝜓) ∧ ∃*𝑥 ∈ 𝐴 𝜑) ↔ (∀𝑥 ∈ 𝐴 (𝜑 → 𝜓) ∧ ∃!𝑥 ∈ 𝐴 𝜑))
 
20-Jul-2026alsanmo 50850 An "all some" statement conjoined with the claim that at most one 𝑥 satisfies its antecedent is equivalent to the universal part conjoined with the claim that exactly one 𝑥 satisfies the antecedent. The "all some" quantifier supplies the existence of such an 𝑥 and ∃*𝑥𝜑 supplies the at-most-one part, so together they yield ∃!𝑥𝜑. (Contributed by Peter Mazsa and David A. Wheeler, 20-Jul-2026.)
((∀∃𝑥(𝜑 → 𝜓) ∧ ∃*𝑥𝜑) ↔ (∀𝑥(𝜑 → 𝜓) ∧ ∃!𝑥𝜑))
 
20-Jul-2026rexrals 50849 If a member of 𝐴 satisfying the antecedent exists, then a restricted "all some" statement reduces to its universal part. This is the restricted counterpart of rexals 50855. (Contributed by Peter Mazsa and David A. Wheeler, 20-Jul-2026.)
(∃𝑥 ∈ 𝐴 𝜑 → (∀∃𝑥 ∈ 𝐴(𝜑 → 𝜓) ↔ ∀𝑥 ∈ 𝐴 (𝜑 → 𝜓)))
 
20-Jul-2026ralrals 50848 If the universal part of a restricted "all some" statement holds, then the statement reduces to the existence of a member of 𝐴 satisfying its antecedent. This is the restricted counterpart of ralals 50854. (Contributed by Peter Mazsa and David A. Wheeler, 20-Jul-2026.)
(∀𝑥 ∈ 𝐴 (𝜑 → 𝜓) → (∀∃𝑥 ∈ 𝐴(𝜑 → 𝜓) ↔ ∃𝑥 ∈ 𝐴 𝜑))
 
20-Jul-2026tgaltai 29427 Parallelism implies alternate angles congruence: if a line (𝑋𝐿𝑍) crosses two parallel lines (𝑋𝐿𝑌) and (𝑍𝐿𝑊), then the alternate angles are congruent. First direction of Theorem 12.21 of [Schwabhauser] p. 126. This is also Proposition 1.29 of Euclid's Elements . (Contributed by Thierry Arnoux, 20-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ (𝑋𝐿𝑍)) ∧ 𝑏 ∈ (𝑃 ∖ (𝑋𝐿𝑍))) ∧ ∃𝑡 ∈ (𝑋𝐿𝑍)𝑡 ∈ (𝑎𝐼𝑏))}    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐺 ∈ TarskiGE)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → (𝑋𝐿𝑌) ∥ (𝑍𝐿𝑊))    &   (𝜑 → 𝑌𝑂𝑊)    &   (𝜑 → 𝑋 ≠ 𝑍)    ⇒   (𝜑 → ⟨“𝑌𝑋𝑍”⟩(cgrA‘𝐺)⟨“𝑊𝑍𝑋”⟩)
 
20-Jul-2026quadcgrprlng 29426 Nontrivial quadrilaterals with congruent and parallel opposite sides are parallelograms. Theorem 12.20 of [Schwabhauser] p. 126. (Contributed by Thierry Arnoux, 20-Jul-2026.)
𝑃 = (Base‘𝐺)    &    − = (dist‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ (𝑋𝐿𝑍)) ∧ 𝑏 ∈ (𝑃 ∖ (𝑋𝐿𝑍))) ∧ ∃𝑡 ∈ (𝑋𝐿𝑍)𝑡 ∈ (𝑎𝐼𝑏))}    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐺 ∈ TarskiGE)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → ¬ (𝑋 ∈ (𝑌𝐿𝑍) ∨ 𝑌 = 𝑍))    &   (𝜑 → (𝑋𝐿𝑌) ∥ (𝑍𝐿𝑊))    &   (𝜑 → (𝑋 − 𝑌) = (𝑍 − 𝑊))    &   (𝜑 → 𝑌𝑂𝑊)    ⇒   (𝜑 → ((𝑌𝐿𝑍) ∥ (𝑊𝐿𝑋) ∧ (𝑌 − 𝑍) = (𝑊 − 𝑋)))
 
20-Jul-2026prlngsymquadopp 29425 In parallelograms, opposing vertices are on opposite sides of the diagonal. Second part of Theorem 12.19 of [Schwabhauser] p. 126. (Contributed by Thierry Arnoux, 20-Jul-2026.)
𝑃 = (Base‘𝐺)    &    − = (dist‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐺 ∈ TarskiGE)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → ¬ (𝑋 ∈ (𝑌𝐿𝑍) ∨ 𝑌 = 𝑍))    &   (𝜑 → (𝑋𝐿𝑌) ∥ (𝑍𝐿𝑊))    &   (𝜑 → (𝑌𝐿𝑍) ∥ (𝑊𝐿𝑋))    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ (𝑋𝐿𝑍)) ∧ 𝑏 ∈ (𝑃 ∖ (𝑋𝐿𝑍))) ∧ ∃𝑡 ∈ (𝑋𝐿𝑍)𝑡 ∈ (𝑎𝐼𝑏))}    &   𝐼 = (Itv‘𝐺)    ⇒   (𝜑 → 𝑊𝑂𝑌)
 
20-Jul-2026prlngsymquad 29424 All parallelograms are symmetric quadrilaterals. First part of Theorem 12.19 of [Schwabhauser] p. 126. (Contributed by Thierry Arnoux, 20-Jul-2026.)
𝑃 = (Base‘𝐺)    &    − = (dist‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐺 ∈ TarskiGE)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → ¬ (𝑋 ∈ (𝑌𝐿𝑍) ∨ 𝑌 = 𝑍))    &   (𝜑 → (𝑋𝐿𝑌) ∥ (𝑍𝐿𝑊))    &   (𝜑 → (𝑌𝐿𝑍) ∥ (𝑊𝐿𝑋))    ⇒   (𝜑 → ((𝑋 − 𝑌) = (𝑍 − 𝑊) ∧ (𝑌 − 𝑍) = (𝑊 − 𝑋)))
 
20-Jul-2026prlngsymquadlem 29423 Lemma for prlngsymquad 29424. (Contributed by Thierry Arnoux, 20-Jul-2026.)
𝑃 = (Base‘𝐺)    &    − = (dist‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐺 ∈ TarskiGE)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → ¬ (𝑋 ∈ (𝑌𝐿𝑍) ∨ 𝑌 = 𝑍))    &   (𝜑 → (𝑋𝐿𝑌) ∥ (𝑍𝐿𝑊))    &   (𝜑 → (𝑌𝐿𝑍) ∥ (𝑊𝐿𝑋))    &   𝑇 = (((pInvG‘𝐺)‘(𝑋(midG‘𝐺)𝑍))‘𝑌)    ⇒   (𝜑 → 𝑇 = 𝑊)
 
20-Jul-2026symquadprlng 29422 Symmetrical quadrilaterals are parallelograms. Theorem 12.18 of [Schwabhauser] p. 126. (Contributed by Thierry Arnoux, 20-Jul-2026.)
𝑃 = (Base‘𝐺)    &    − = (dist‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐺 ∈ TarskiGE)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → (𝑋 − 𝑌) = (𝑍 − 𝑊))    &   (𝜑 → (𝑌 − 𝑍) = (𝑊 − 𝑋))    &   (𝜑 → ¬ (𝑋 ∈ (𝑌𝐿𝑍) ∨ 𝑌 = 𝑍))    &   (𝜑 → 𝑌 ≠ 𝑊)    &   (𝜑 → 𝑇 ∈ (𝑋𝐿𝑍))    &   (𝜑 → 𝑇 ∈ (𝑌𝐿𝑊))    ⇒   (𝜑 → ((𝑋𝐿𝑌) ∥ (𝑍𝐿𝑊) ∧ (𝑌𝐿𝑍) ∥ (𝑊𝐿𝑋)))
 
20-Jul-2026prlngeq 29417 Playfair's axiom, written as an equality: if two different lines are parallel to a given line at a given point, they are equal. (Contributed by Thierry Arnoux, 20-Jul-2026.)
𝑃 = (Base‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐺 ∈ TarskiGE)    &   (𝜑 → 𝐴 ∥ 𝐵)    &   (𝜑 → 𝐴 ∥ 𝐶)    &   (𝜑 → 𝑋 ∈ 𝐵)    &   (𝜑 → 𝑋 ∈ 𝐶)    ⇒   (𝜑 → 𝐵 = 𝐶)
 
20-Jul-2026df-angmgm 29356 Definition of the angle addition magma. See following theorems for better readable properties. Because the textbook's definition of angle congruence does not consider orientation (cf. cgraswap 29309) , our notion of angle does not include reflex angles (angles larger than a straight angle). Therefore, like with ℕ0, at this point, we can only build a magma , which is e.g. not isomorphic with the rotation group SO(2) . (Contributed by Thierry Arnoux, 20-Jul-2026.)
AngMgm = (𝑔 ∈ V ↦ ⦋(Base‘𝑔) / 𝑝⦌⦋{𝑑 ∈ (𝑝 ↑m (0..^3)) ∣ ((𝑑‘0) ≠ (𝑑‘1) ∧ (𝑑‘1) ≠ (𝑑‘2))} / 𝑎⦌({⟨(Base‘ndx), 𝑎⟩, ⟨(+g‘ndx), (𝑒 ∈ 𝑎, 𝑓 ∈ 𝑎 ↦ if((𝑒‘0) ∈ ((𝑒‘1)(LineG‘𝑔)(𝑒‘2)), ⟨“(𝑓‘0)(𝑓‘1)(℩𝑧 ∈ 𝑝 (⟨“(𝑓‘2)(𝑓‘1)𝑧”⟩(cgrA‘𝑔)𝑒 ∧ ((𝑓‘1)(dist‘𝑔)𝑧) = ((𝑒‘1)(dist‘𝑔)(𝑒‘0))))”⟩, ⟨“(𝑒‘0)(𝑒‘1)(℩𝑧 ∈ 𝑝 (⟨“(𝑒‘2)(𝑒‘1)𝑧”⟩(cgrA‘𝑔)𝑓 ∧ ((𝑒‘1)(dist‘𝑔)𝑧) = ((𝑓‘1)(dist‘𝑔)(𝑓‘0)) ∧ (((𝑒‘1)(LineG‘𝑔)(𝑒‘2)) ∩ (𝑧(Itv‘𝑔)(𝑒‘0))) ≠ ∅))”⟩))⟩, ⟨(le‘ndx), (≤∠‘𝑔)⟩} /s (cgrA‘𝑔)))
 
20-Jul-2026symquadmid 29286 In a symmetrical quadrilateral, the midpoints of the diagonals coincide. Corollary of Lemma 7.21 of [Schwabhauser] p. 52. (Contributed by Thierry Arnoux, 20-Jul-2026.)
𝑃 = (Base‘𝐺)    &    − = (dist‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝑀 = (midG‘𝐺)    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ (𝑋𝐿𝑍)) ∧ 𝑏 ∈ (𝑃 ∖ (𝑋𝐿𝑍))) ∧ ∃𝑡 ∈ (𝑋𝐿𝑍)𝑡 ∈ (𝑎𝐼𝑏))}    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → ¬ (𝑋 ∈ (𝑌𝐿𝑍) ∨ 𝑌 = 𝑍))    &   (𝜑 → 𝑌 ≠ 𝑊)    &   (𝜑 → (𝑋 − 𝑌) = (𝑍 − 𝑊))    &   (𝜑 → (𝑌 − 𝑍) = (𝑊 − 𝑋))    &   (𝜑 → 𝑌𝑂𝑊)    ⇒   (𝜑 → (𝑋𝑀𝑍) = (𝑌𝑀𝑊))
 
20-Jul-2026hlopp 29232 If two points 𝑋 and 𝑌 lie on opposite sides of a line 𝐴, then given a point 𝑍 on 𝐴, any point 𝑊 on the line (𝑋𝐿𝑍) opposite to 𝑌 lies on the half line (𝑍𝑋) (Contributed by Thierry Arnoux, 20-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ 𝐴) ∧ 𝑏 ∈ (𝑃 ∖ 𝐴)) ∧ ∃𝑡 ∈ 𝐴 𝑡 ∈ (𝑎𝐼𝑏))}    &   𝐾 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑋𝑂𝑌)    &   (𝜑 → 𝑍 ∈ 𝐴)    &   (𝜑 → 𝑊𝑂𝑌)    &   (𝜑 → 𝑊 ∈ (𝑋𝐿𝑍))    ⇒   (𝜑 → 𝑊(𝐾‘𝑍)𝑋)
 
20-Jul-2026symquadprlnglem 29147 Lemma for symquadprlnglem 29147. (Contributed by Thierry Arnoux, 20-Jul-2026.)
𝑃 = (Base‘𝐺)    &    − = (dist‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → (𝑋 − 𝑌) = (𝑍 − 𝑊))    &   (𝜑 → (𝑌 − 𝑍) = (𝑊 − 𝑋))    &   (𝜑 → ¬ (𝑋 ∈ (𝑌𝐿𝑍) ∨ 𝑌 = 𝑍))    &   (𝜑 → 𝑌 ≠ 𝑊)    &   (𝜑 → 𝑇 ∈ (𝑋𝐿𝑍))    &   (𝜑 → 𝑇 ∈ (𝑌𝐿𝑊))    ⇒   (𝜑 → ¬ (𝑊 ∈ (𝑍𝐿𝑌) ∨ 𝑍 = 𝑌))
 
20-Jul-2026crng4 20468 Commutative/associative law for commutative rings. See also mul4d 11503. (Contributed by Jeff Madsen, 19-Jun-2010.) (Revised by AV, 20-Jul-2026.)
𝐵 = (Base‘𝑅)    &    · = (.r‘𝑅)    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝑋 ∈ 𝐵)    &   (𝜑 → 𝑌 ∈ 𝐵)    &   (𝜑 → 𝑍 ∈ 𝐵)    &   (𝜑 → 𝑈 ∈ 𝐵)    ⇒   (𝜑 → ((𝑋 · 𝑌) · (𝑍 · 𝑈)) = ((𝑋 · 𝑍) · (𝑌 · 𝑈)))
 
19-Jul-2026crngrhmfo 20706 The image of a surjective homomorphism from a commutative ring is commutative. (Contributed by Jeff Madsen, 4-Jan-2011.) (Revised by AV, 19-Jul-2026.)
𝐵 = (Base‘𝑆)    ⇒   ((𝑅 ∈ CRing ∧ 𝐹 ∈ (𝑅 RingHom 𝑆) ∧ 𝐹:dom 𝐹–onto→𝐵) → 𝑆 ∈ CRing)
 
19-Jul-2026karden 9940 If we allow the Axiom of Regularity, we can avoid the Axiom of Choice by defining the cardinal number of a set as the set of all sets equinumerous to it and having the least possible rank. This theorem proves the equinumerosity relationship for this definition (compare carden 10616). The hypotheses correspond to the definition of kard of [Enderton] p. 222 (which we don't define separately since currently we do not use it elsewhere). This theorem along with kardex 9938 justify the definition of kard. The restriction to the least rank prevents the proper class that would result from {𝑥 ∣ 𝑥 ≈ 𝐴}. (Contributed by NM, 18-Dec-2003.) (Revised by AV, 12-Jul-2022.) Use the Scott operation. (Revised by BTernaryTau, 19-Jul-2026.)
𝐴 ∈ V    &   𝐶 = Scott {𝑥 ∣ 𝑥 ≈ 𝐴}    &   𝐷 = Scott {𝑥 ∣ 𝑥 ≈ 𝐵}    ⇒   (𝐶 = 𝐷 ↔ 𝐴 ≈ 𝐵)
 
19-Jul-2026kardex 9938 The collection of all sets equinumerous to a set 𝐴 and having the least possible rank is a set. This is the part of the justification of the definition of kard of [Enderton] p. 222. (Contributed by NM, 14-Dec-2003.) Use the Scott operation. (Revised by BTernaryTau, 19-Jul-2026.)
Scott {𝑥 ∣ 𝑥 ≈ 𝐴} ∈ V
 
19-Jul-2026cplem2 9933 Lemma for the Collection Principle cp 9935. (Contributed by NM, 17-Oct-2003.) Use the Scott operation. (Revised by BTernaryTau, 19-Jul-2026.)
𝐴 ∈ V    ⇒   ∃𝑦∀𝑥 ∈ 𝐴 (𝐵 ≠ ∅ → (𝐵 ∩ 𝑦) ≠ ∅)
 
19-Jul-2026cplem1 9931 Lemma for the Collection Principle cp 9935. (Contributed by NM, 17-Oct-2003.) Use the Scott operation. (Revised by BTernaryTau, 19-Jul-2026.)
𝐶 = ∪ 𝑥 ∈ 𝐴 Scott 𝐵    ⇒   ∀𝑥 ∈ 𝐴 (𝐵 ≠ ∅ → (𝐵 ∩ 𝐶) ≠ ∅)
 
19-Jul-2026scott0b 9918 Applying Scott's trick yields the empty set iff it was applied to the empty set. (Contributed by NM, 15-Oct-2003.) Use the Scott operation. (Revised by BTernaryTau, 19-Jul-2026.)
(𝐴 = ∅ ↔ Scott 𝐴 = ∅)
 
19-Jul-2026disjdifg 4425 A class does not intersect a relative complement of a superclass. (Contributed by NM, 24-Mar-1998.) Generalize from disjdif 4426. (Revised by BJ, 19-Jul-2026.)
(𝐴 ⊆ 𝐵 → (𝐴 ∩ (𝐶 ∖ 𝐵)) = ∅)
 
19-Jul-2026sseq0b 4353 The only subclass of the empty class is itself. (Contributed by NM, 7-Mar-2007.) Strengthen sseq0 4354 to a biconditional. (Revised by BJ, 19-Jul-2026.)
(𝐴 = ∅ → (𝐵 ⊆ 𝐴 ↔ 𝐵 = ∅))
 
18-Jul-2026scottex 9914 Scott's trick produces a set. (Contributed by NM, 13-Oct-2003.) Use the Scott operation. (Revised by BTernaryTau, 18-Jul-2026.)
Scott 𝐴 ∈ V
 
18-Jul-2026sepab 5294 Separation Scheme (Aussonderung) in terms of a class abstraction. Prefer using the more natural statement rabexg 5299. (Contributed by NM, 8-Jun-1994.) Put in closed form. (Revised by BJ, 18-Jul-2026.)
(𝐴 ∈ 𝑉 → {𝑥 ∣ (𝑥 ∈ 𝐴 ∧ 𝜑)} ∈ V)
 
18-Jul-2026ssex 5282 A subclass of a set is a set. Exercise 3 of [TakeutiZaring] p. 22. This is one way to express the Axiom of Separation ax-sep 5249 (a.k.a. Subset Axiom). (Contributed by NM, 27-Apr-1994.) (Proof shortened by BJ, 18-Jul-2026.)
𝐵 ∈ V    ⇒   (𝐴 ⊆ 𝐵 → 𝐴 ∈ V)
 
18-Jul-2026ssexg 5281 A subclass of a set is a set. Exercise 3 of [TakeutiZaring] p. 22 (generalized). (Contributed by NM, 14-Aug-1994.) (Proof shortened by BJ, 18-Jul-2026.)
((𝐴 ⊆ 𝐵 ∧ 𝐵 ∈ 𝐶) → 𝐴 ∈ V)
 
18-Jul-2026inssdif0 4322 Intersection, subclass, and difference relationship. (Contributed by NM, 27-Oct-1996.) (Proof shortened by Andrew Salmon, 26-Jun-2011.) (Proof shortened by Wolf Lammen, 30-Sep-2014.) (Proof shortened by BJ, 18-Jul-2026.)
((𝐴 ∩ 𝐵) ⊆ 𝐶 ↔ (𝐴 ∩ (𝐵 ∖ 𝐶)) = ∅)
 
16-Jul-2026nmulle 36936 A condition for bounding a natural product above. Converse of ltnmul 36935. (Contributed by Scott Fenton, 16-Jul-2026.)
((𝐴 ∈ On ∧ 𝐵 ∈ On ∧ 𝐶 ∈ On) → ((𝐴 ·no 𝐵) ⊆ 𝐶 ↔ ∀𝑎 ∈ 𝐴 ∀𝑏 ∈ 𝐵 ((𝑎 ·no 𝐵) +no (𝐴 ·no 𝑏)) ∈ (𝐶 +no (𝑎 ·no 𝑏))))
 
15-Jul-20262alsraln0id 50858 Nested general "all some" quantifiers with class membership as their antecedents, for the same class 𝐴: 𝜑 holds for every 𝑥 and every 𝑦 in 𝐴, and 𝐴 is not empty. (Contributed by Peter Mazsa, 28-May-2019.) (Revised by David A. Wheeler, 15-Jul-2026.)
(∀∃𝑥(𝑥 ∈ 𝐴 → ∀∃𝑦(𝑦 ∈ 𝐴 → 𝜑)) ↔ (∀𝑥 ∈ 𝐴 ∀𝑦 ∈ 𝐴 𝜑 ∧ 𝐴 ≠ ∅))
 
15-Jul-20262alsraln0 50857 Nested general "all some" quantifiers with class membership as their antecedents: 𝜑 holds for every 𝑥 in 𝐴 and every 𝑦 in 𝐵, and both 𝐴 and 𝐵 are not empty. (Contributed by Peter Mazsa, 28-May-2019.) (Revised by David A. Wheeler, 15-Jul-2026.)
(∀∃𝑥(𝑥 ∈ 𝐴 → ∀∃𝑦(𝑦 ∈ 𝐵 → 𝜑)) ↔ (∀𝑥 ∈ 𝐴 ∀𝑦 ∈ 𝐵 𝜑 ∧ (𝐴 ≠ ∅ ∧ 𝐵 ≠ ∅)))
 
15-Jul-2026n0als 50856 If 𝐴 is not empty, then the general "all some" quantifier with class membership as its antecedent reduces to the assertion that 𝜑 holds for every 𝑥 in 𝐴. (Contributed by Peter Mazsa, 19-Dec-2018.) (Revised by David A. Wheeler, 15-Jul-2026.)
(𝐴 ≠ ∅ → (∀∃𝑥(𝑥 ∈ 𝐴 → 𝜑) ↔ ∀𝑥 ∈ 𝐴 𝜑))
 
15-Jul-2026rexals 50855 If some 𝑥 in 𝐴 satisfies 𝜑, then the general "all some" quantifier with class membership as its antecedent reduces to the assertion that 𝜑 holds for every 𝑥 in 𝐴. See rexrals 50849 for the restricted counterpart. (Contributed by Peter Mazsa, 19-Dec-2018.) (Revised by David A. Wheeler, 15-Jul-2026.)
(∃𝑥 ∈ 𝐴 𝜑 → (∀∃𝑥(𝑥 ∈ 𝐴 → 𝜑) ↔ ∀𝑥 ∈ 𝐴 𝜑))
 
15-Jul-2026ralals 50854 If 𝜑 holds for every 𝑥 in 𝐴, then the general "all some" quantifier with class membership as its antecedent reduces to the assertion that some 𝑥 in 𝐴 satisfies 𝜑. See ralrals 50848 for the restricted counterpart. (Contributed by Peter Mazsa, 19-Dec-2018.) (Revised by David A. Wheeler, 15-Jul-2026.)
(∀𝑥 ∈ 𝐴 𝜑 → (∀∃𝑥(𝑥 ∈ 𝐴 → 𝜑) ↔ ∃𝑥 ∈ 𝐴 𝜑))
 
15-Jul-2026alsraln0 50853 The general "all some" quantifier with class membership as its antecedent holds if and only if 𝜑 holds for every 𝑥 in 𝐴 and 𝐴 is not empty. (Contributed by Peter Mazsa, 28-Nov-2018.) (Revised by David A. Wheeler, 15-Jul-2026.)
(∀∃𝑥(𝑥 ∈ 𝐴 → 𝜑) ↔ (∀𝑥 ∈ 𝐴 𝜑 ∧ 𝐴 ≠ ∅))
 
15-Jul-2026alsralrex 50852 The general "all some" quantifier with class membership as its antecedent holds if and only if 𝜑 holds for every 𝑥 in 𝐴 and some 𝑥 in 𝐴 satisfies 𝜑. (Contributed by Peter Mazsa, 27-Nov-2018.) (Revised by David A. Wheeler, 15-Jul-2026.)
(∀∃𝑥(𝑥 ∈ 𝐴 → 𝜑) ↔ (∀𝑥 ∈ 𝐴 𝜑 ∧ ∃𝑥 ∈ 𝐴 𝜑))
 
15-Jul-2026ltnmul 36935 Characterize less-than a natural product. (Contributed by Scott Fenton, 15-Jul-2026.)
((𝐴 ∈ On ∧ 𝐵 ∈ On ∧ 𝐶 ∈ On) → (𝐴 ∈ (𝐵 ·no 𝐶) ↔ ∃𝑏 ∈ 𝐵 ∃𝑐 ∈ 𝐶 (𝐴 +no (𝑏 ·no 𝑐)) ⊆ ((𝑏 ·no 𝐶) +no (𝐵 ·no 𝑐))))
 
15-Jul-2026nmulel1 36934 Natural multiplication by a non-zero number preserves less-than. (Contributed by Scott Fenton, 15-Jul-2026.)
(((𝐵 ∈ On ∧ 𝐶 ∈ On) ∧ (𝐴 ∈ 𝐵 ∧ 𝐶 ≠ ∅)) → (𝐶 ·no 𝐴) ∈ (𝐶 ·no 𝐵))
 
15-Jul-2026nmulss1 36933 Natural multiplication preserves less-than or equal. (Contributed by Scott Fenton, 15-Jul-2026.)
(((𝐴 ∈ On ∧ 𝐵 ∈ On ∧ 𝐶 ∈ On) ∧ 𝐴 ⊆ 𝐵) → (𝐶 ·no 𝐴) ⊆ (𝐶 ·no 𝐵))
 
15-Jul-2026nmuladdss 36932 Ordering relationship for natural ordinal operations. (Contributed by Scott Fenton, 15-Jul-2026.)
(((𝐴 ∈ On ∧ 𝐵 ∈ On) ∧ (𝐶 ∈ On ∧ 𝐷 ∈ On) ∧ (𝐶 ⊆ 𝐴 ∧ 𝐷 ⊆ 𝐵)) → ((𝐶 ·no 𝐵) +no (𝐴 ·no 𝐷)) ⊆ ((𝐴 ·no 𝐵) +no (𝐶 ·no 𝐷)))
 
15-Jul-2026nmuladdel 36931 Ordering relationship for natural ordinal operations. (Contributed by Scott Fenton, 15-Jul-2026.)
(((𝐴 ∈ On ∧ 𝐵 ∈ On) ∧ (𝐶 ∈ 𝐴 ∧ 𝐷 ∈ 𝐵)) → ((𝐶 ·no 𝐵) +no (𝐴 ·no 𝐷)) ∈ ((𝐴 ·no 𝐵) +no (𝐶 ·no 𝐷)))
 
14-Jul-2026bj-inex1gALT 37807 Proof of inex1g 5279 from sepg 5251 to then allow proving inex1 5277 from it. That does not reduce the combined proof size of inex1 5277 and inex1g 5279. (Contributed by BJ, 14-Jul-2026.) (Proof modification is discouraged.) (New usage is discouraged.)
(𝐴 ∈ 𝑉 → (𝐴 ∩ 𝐵) ∈ V)
 
14-Jul-2026uniex2 7743 The Axiom of Union using the standard abbreviation for union. Given any set 𝑥, its union 𝑦 exists. (Contributed by NM, 4-Jun-2006.) (Proof shortened by BJ, 14-Jul-2026.)
∃𝑦 𝑦 = ∪ 𝑥
 
14-Jul-2026sepgi 5252 Inference associated with sepg 5251. The requirement that 𝑦 not occur in 𝜑 is necessary, as notsep 5325 shows. (Contributed by NM, 21-Jun-1993.) (Revised by BJ, 14-Jul-2026.)
𝐴 ∈ V    ⇒   ∃𝑦∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝐴 ∧ 𝜑))
 
13-Jul-2026idomcanr 49389 Cancellation law for domains. (Contributed by Jeff Madsen, 6-Jan-2011.) (Revised by AV, 13-Jul-2026.)
𝐵 = (Base‘𝑅)    &    · = (.r‘𝑅)    &    0 = (0g‘𝑅)    ⇒   (((𝑅 ∈ IDomn ∧ (𝑋 ∈ 𝐵 ∧ 𝑌 ∈ 𝐵 ∧ 𝑍 ∈ 𝐵)) ∧ 𝑍 ≠ 0 ) → ((𝑋 · 𝑍) = (𝑌 · 𝑍) → 𝑋 = 𝑌))
 
13-Jul-2026idomcanl 49388 Cancellation law for domains. (Contributed by Jeff Madsen, 6-Jan-2011.) (Revised by AV, 13-Jul-2026.)
𝐵 = (Base‘𝑅)    &    · = (.r‘𝑅)    &    0 = (0g‘𝑅)    ⇒   (((𝑅 ∈ IDomn ∧ (𝑋 ∈ 𝐵 ∧ 𝑌 ∈ 𝐵 ∧ 𝑍 ∈ 𝐵)) ∧ 𝑋 ≠ 0 ) → ((𝑋 · 𝑌) = (𝑋 · 𝑍) → 𝑌 = 𝑍))
 
13-Jul-2026prlngmid2 29421 If the midpoints of two segments (𝑋𝐼𝑍) and (𝑌𝐼𝑊) coincide, the points 𝑋, 𝑌, 𝑍 and 𝑊 form a parallelogram, i.e. the lines (𝑋𝐿𝑌) and (𝑍𝐿𝑊) are parallel. Theorem 12.17 of [Schwabhauser] p. 125. (Contributed by Thierry Arnoux, 13-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   𝑀 = (midG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐺 ∈ TarskiGE)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ (𝑃 ∖ (𝑋𝐿𝑌)))    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → (𝑋𝑀𝑍) = (𝑌𝑀𝑊))    &   (𝜑 → 𝑋 ≠ 𝑌)    ⇒   (𝜑 → (𝑋𝐿𝑌) ∥ (𝑍𝐿𝑊))
 
13-Jul-2026prlnginn0 29420 A line 𝐶 intersecting another line 𝐴 also intersects any line 𝐵 parallel to 𝐴. Theorem 12.16 of [Schwabhauser] p. 125. (Contributed by Thierry Arnoux, 13-Jul-2026.)
𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐺 ∈ TarskiGE)    &   (𝜑 → 𝐻 ∈ ran 𝐸)    &   (𝜑 → 𝐶 ∈ ran 𝐿)    &   (𝜑 → (𝐴 ∩ 𝐶) ≠ ∅)    &   (𝜑 → 𝐴 ≠ 𝐶)    &   (𝜑 → 𝐴 ∥ 𝐵)    &   (𝜑 → 𝐴 ⊆ 𝐻)    &   (𝜑 → 𝐵 ⊆ 𝐻)    &   (𝜑 → 𝐶 ⊆ 𝐻)    ⇒   (𝜑 → (𝐵 ∩ 𝐶) ≠ ∅)
 
13-Jul-2026prlngplngtr 29419 Transitivity of parallelism, for lines in the same plane 𝐻. This is case 1 of Theorem 12.15 of [Schwabhauser] p. 124. (Contributed by Thierry Arnoux, 13-Jul-2026.)
𝐸 = (hlG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐻 ∈ ran 𝐸)    &   (𝜑 → 𝐴 ⊆ 𝐻)    &   (𝜑 → 𝐴 ∥ 𝐵)    &   (𝜑 → 𝐺 ∈ TarskiGE)    &   (𝜑 → 𝐶 ⊆ 𝐻)    &   (𝜑 → 𝐵 ∥ 𝐶)    ⇒   (𝜑 → 𝐴 ∥ 𝐶)
 
13-Jul-2026prlngpln4 29418 Building a parallel line conserves planes, i.e. given a line 𝐴 and a point 𝑋 not on 𝐴, the (unique) parallel 𝐵 to 𝐴 through 𝑋 lies completely within the plane defined by 𝐴 and 𝑋. Theorem 12.14 of [Schwabhauser] p. 124. (Contributed by Thierry Arnoux, 13-Jul-2026.)
𝐸 = (hlG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐻 ∈ ran 𝐸)    &   (𝜑 → 𝐴 ⊆ 𝐻)    &   (𝜑 → 𝐴 ∥ 𝐵)    &   (𝜑 → 𝑋 ∈ 𝐻)    &   (𝜑 → 𝑋 ∈ 𝐵)    ⇒   (𝜑 → 𝐵 ⊆ 𝐻)
 
13-Jul-2026prlngmo2 29416 Playfair's axiom, without the restriction that the point 𝑋 is outside of the line 𝐴. Theorem 12.11 of [Schwabhauser] p. 123. (Contributed by Thierry Arnoux, 13-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝐺 ∈ TarskiGE)    ⇒   (𝜑 → ∃*𝑏 ∈ ran 𝐿(𝐴 ∥ 𝑏 ∧ 𝑋 ∈ 𝑏))
 
13-Jul-2026dfprlng3 29408 Alternate definition of (strict) parallelism. Theorem 12.7 of [Schwabhauser] p. 122. (Contributed by Thierry Arnoux, 13-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ (𝑃 ∖ {𝑋}))    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝐴 ≠ (𝑋𝐿𝑌))    ⇒   (𝜑 → (𝐴 ∥ (𝑋𝐿𝑌) ↔ (𝑋((hpG‘𝐺)‘𝐴)𝑌 ∧ (𝐴 ∩ (𝑋𝐿𝑌)) = ∅)))
 
13-Jul-2026dfprlng2 29407 Alternate definition of (strict) parallelism. Theorem 12.7 of [Schwabhauser] p. 122. (Contributed by Thierry Arnoux, 13-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ (𝑃 ∖ {𝑋}))    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ (𝑃 ∖ {𝑍}))    &   (𝜑 → (𝑋𝐿𝑌) ≠ (𝑍𝐿𝑊))    ⇒   (𝜑 → ((𝑋𝐿𝑌) ∥ (𝑍𝐿𝑊) ↔ (𝑍((hpG‘𝐺)‘(𝑋𝐿𝑌))𝑊 ∧ ((𝑋𝐿𝑌) ∩ (𝑍𝐿𝑊)) = ∅)))
 
13-Jul-2026ragsupplcgra 29327 An angle ⟨“𝑋𝑌𝑍”⟩ is a right angle exactly when it is congruent to its supplementary angle ⟨“𝑋𝑌𝑊”⟩. Theorem 11.18 of [Schwabhauser] p. 98. (Contributed by Thierry Arnoux, 13-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ (𝑃 ∖ {𝑌}))    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ (𝑃 ∖ {𝑌}))    &   (𝜑 → 𝑊 ∈ (𝑃 ∖ {𝑌}))    &   (𝜑 → 𝑌 ∈ (𝑍𝐼𝑊))    ⇒   (𝜑 → (⟨“𝑋𝑌𝑍”⟩ ∈ (∟G‘𝐺) ↔ ⟨“𝑋𝑌𝑍”⟩(cgrA‘𝐺)⟨“𝑋𝑌𝑊”⟩))
 
13-Jul-2026cgrarag 29326 Any angle ⟨“𝐴𝐵𝐶”⟩ congruent with a right angle ⟨“𝑋𝑌𝑍”⟩ is a right angle. Theorem 11.17 of [Schwabhauser] p. 98. (Contributed by Thierry Arnoux, 13-Jul-2026.)
𝑃 = (Base‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝐴 ∈ 𝑃)    &   (𝜑 → 𝐵 ∈ 𝑃)    &   (𝜑 → 𝐶 ∈ 𝑃)    &   (𝜑 → ⟨“𝑋𝑌𝑍”⟩ ∈ (∟G‘𝐺))    &   (𝜑 → ⟨“𝑋𝑌𝑍”⟩(cgrA‘𝐺)⟨“𝐴𝐵𝐶”⟩)    ⇒   (𝜑 → ⟨“𝐴𝐵𝐶”⟩ ∈ (∟G‘𝐺))
 
13-Jul-2026mirlni 29149 The mirror of a point 𝑋 on a line (𝑌𝐿𝑍) is on the mirrored line ((𝑀‘𝑌)𝐿(𝑀‘𝑍)). (Contributed by Thierry Arnoux, 13-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝑆 = (pInvG‘𝐺)    &   𝑀 = (𝑆‘𝐴)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑍 ≠ 𝑌)    &   (𝜑 → 𝑋 ∈ (𝑌𝐿𝑍))    ⇒   (𝜑 → (𝑀‘𝑋) ∈ ((𝑀‘𝑌)𝐿(𝑀‘𝑍)))
 
13-Jul-2026mirleqb 29148 Equality theorem for point mirroring. (Contributed by Thierry Arnoux, 13-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝑆 = (pInvG‘𝐺)    &   𝑀 = (𝑆‘𝐴)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ 𝑃)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    ⇒   (𝜑 → (𝑋 = 𝑌 ↔ (𝑀‘𝑋) = (𝑀‘𝑌)))
 
13-Jul-2026hlgrcl2 29049 Reverse closure for rays. (Contributed by Thierry Arnoux, 13-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐾 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ 𝑉)    &   (𝜑 → 𝐶 ∈ 𝑃)    &   (𝜑 → 𝐴(𝐾‘𝐶)𝐵)    ⇒   (𝜑 → 𝐵 ∈ 𝑃)
 
13-Jul-2026hlgrcl1 29048 Reverse closure for rays. (Contributed by Thierry Arnoux, 13-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐾 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ 𝑉)    &   (𝜑 → 𝐶 ∈ 𝑃)    &   (𝜑 → 𝐴(𝐾‘𝐶)𝐵)    ⇒   (𝜑 → 𝐴 ∈ 𝑃)
 
13-Jul-2026ishlg2 29047 Alternate version of ishlg 29050, including closure. (Contributed by Thierry Arnoux, 13-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐾 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ 𝑉)    &   (𝜑 → 𝐶 ∈ 𝑃)    ⇒   (𝜑 → (𝐴(𝐾‘𝐶)𝐵 ↔ ((𝐴 ∈ 𝑃 ∧ 𝐵 ∈ 𝑃) ∧ (𝐴 ≠ 𝐶 ∧ 𝐵 ≠ 𝐶 ∧ (𝐴 ∈ (𝐶𝐼𝐵) ∨ 𝐵 ∈ (𝐶𝐼𝐴))))))
 
13-Jul-2026eldifsnbd 4749 Membership in a set with an element removed implies non-equality with that element. (Contributed by Thierry Arnoux, 13-Jul-2026.)
(𝜑 → 𝐴 ∈ (𝐵 ∖ {𝐶}))    ⇒   (𝜑 → 𝐴 ≠ 𝐶)
 
13-Jul-2026nrmod 3839 Deduce the negation of a restricted "at most one" quantifier. (Contributed by Thierry Arnoux, 13-Jul-2026.)
(𝑥 = 𝑋 → (𝜓 ↔ 𝜒))    &   (𝑥 = 𝑌 → (𝜓 ↔ 𝜃))    &   (𝜑 → 𝑋 ∈ 𝐴)    &   (𝜑 → 𝑌 ∈ 𝐴)    &   (𝜑 → 𝜒)    &   (𝜑 → 𝜃)    &   (𝜑 → 𝑋 ≠ 𝑌)    ⇒   (𝜑 → ¬ ∃*𝑥 ∈ 𝐴 𝜓)
 
13-Jul-20263orim123da 1473 Disjoin antecedents and consequents of three premises. (Contributed by Thierry Arnoux, 13-Jul-2026.)
(𝜑 → (𝜓 ∨ 𝜃 ∨ 𝜂))    &   ((𝜑 ∧ 𝜓) → 𝜒)    &   ((𝜑 ∧ 𝜃) → 𝜏)    &   ((𝜑 ∧ 𝜂) → 𝜁)    ⇒   (𝜑 → (𝜒 ∨ 𝜏 ∨ 𝜁))
 
12-Jul-2026rals-no-surprise 50847 Demonstrate that there is never a "surprise" when using the allsome quantifier restricted to a class, that is, it is never possible for the consequent to be both always true and always false of the members of 𝐴 that satisfy the antecedent. This is the restricted counterpart of als-no-surprise 50846, and follows from it by dfrals2 50830. Note that this needs no assumption that 𝐴 is nonempty, because allsome requires a member of 𝐴 satisfying 𝜑, and that member would have to satisfy both 𝜓 and ¬ 𝜓. The ordinary restricted "for all" requires no such member and can be vacuously true, as shown in empty-surprise2 50823; that is the point of allsome. (Contributed by David A. Wheeler, 12-Jul-2026.)
¬ (∀∃𝑥 ∈ 𝐴(𝜑 → 𝜓) ∧ ∀∃𝑥 ∈ 𝐴(𝜑 → ¬ 𝜓))
 
12-Jul-2026cbvals 50845 Rule used to change bound variables, using implicit substitution. (Contributed by David A. Wheeler, 12-Jul-2026.)
(𝑥 = 𝑦 → (𝜑 ↔ 𝜒))    &   (𝑥 = 𝑦 → (𝜓 ↔ 𝜃))    ⇒   (∀∃𝑥(𝜑 → 𝜓) ↔ ∀∃𝑦(𝜒 → 𝜃))
 
12-Jul-2026nfrals 50844 Bound-variable hypothesis builder for "all some" restricted to a class. (Contributed by David A. Wheeler, 12-Jul-2026.)
Ⅎ𝑥𝐴    &   Ⅎ𝑥𝜑    &   Ⅎ𝑥𝜓    ⇒   Ⅎ𝑥∀∃𝑦 ∈ 𝐴(𝜑 → 𝜓)
 
12-Jul-2026nfals 50843 Bound-variable hypothesis builder for "all some". (Contributed by David A. Wheeler, 12-Jul-2026.)
Ⅎ𝑥𝜑    &   Ⅎ𝑥𝜓    ⇒   Ⅎ𝑥∀∃𝑦(𝜑 → 𝜓)
 
12-Jul-2026alsbid 50842 Deduction form of alsbii 50840. (Contributed by David A. Wheeler, 12-Jul-2026.)
Ⅎ𝑥𝜑    &   (𝜑 → (𝜓 ↔ 𝜃))    &   (𝜑 → (𝜒 ↔ 𝜏))    ⇒   (𝜑 → (∀∃𝑥(𝜓 → 𝜒) ↔ ∀∃𝑥(𝜃 → 𝜏)))
 
12-Jul-2026ralsbii 50841 Congruence for "all some" restricted to a class. (Contributed by David A. Wheeler, 12-Jul-2026.)
(𝜑 ↔ 𝜒)    &   (𝜓 ↔ 𝜃)    ⇒   (∀∃𝑥 ∈ 𝐴(𝜑 → 𝜓) ↔ ∀∃𝑥 ∈ 𝐴(𝜒 → 𝜃))
 
12-Jul-2026alsbii 50840 Congruence: equivalents may be substituted inside an "all some". (Contributed by David A. Wheeler, 12-Jul-2026.)
(𝜑 ↔ 𝜒)    &   (𝜓 ↔ 𝜃)    ⇒   (∀∃𝑥(𝜑 → 𝜓) ↔ ∀∃𝑥(𝜒 → 𝜃))
 
12-Jul-2026ralsex 50839 The consequent of an "all some" restricted to a class is witnessed: some member of 𝐴 satisfying 𝜑 also satisfies 𝜓. Restricted counterpart of alsex 50838. (Contributed by David A. Wheeler, 12-Jul-2026.)
(∀∃𝑥 ∈ 𝐴(𝜑 → 𝜓) → ∃𝑥 ∈ 𝐴 𝜓)
 
12-Jul-2026alsex 50838 The consequent of an "all some" is witnessed: if 𝜓 holds of every 𝑥 satisfying 𝜑, and some 𝑥 satisfies 𝜑, then some 𝑥 satisfies 𝜓. This is the positive counterpart of als-no-surprise 50846, and it is the property that ordinary "for all" with implication lacks: from ∀𝑥(𝜑 → 𝜓) alone nothing whatever follows about 𝜓, as alimp-surprise 50820 shows. It is the reason the allsome quantifier says what a speaker of "all Martians are green" usually means. (Contributed by David A. Wheeler, 12-Jul-2026.)
(∀∃𝑥(𝜑 → 𝜓) → ∃𝑥𝜓)
 
12-Jul-2026ralsn0d 50837 Deduction rule: Given "all some" applied to a class, the class is not the empty set. (Contributed by David A. Wheeler, 23-Oct-2018.) (Revised by David A. Wheeler, 12-Jul-2026.)
(𝜑 → ∀∃𝑥 ∈ 𝐴(𝜓 → 𝜒))    ⇒   (𝜑 → 𝐴 ≠ ∅)
 
12-Jul-2026rals2d 50836 Deduction rule: Given "all some" applied to a class, you can extract the "there exists" part. Note that the witness must satisfy the antecedent 𝜓, not merely be a member of 𝐴. (Contributed by David A. Wheeler, 20-Oct-2018.) (Revised by David A. Wheeler, 12-Jul-2026.)
(𝜑 → ∀∃𝑥 ∈ 𝐴(𝜓 → 𝜒))    ⇒   (𝜑 → ∃𝑥 ∈ 𝐴 𝜓)
 
12-Jul-2026rals1d 50835 Deduction rule: Given "all some" applied to a class, you can extract the "for all" part. (Contributed by David A. Wheeler, 20-Oct-2018.) (Revised by David A. Wheeler, 12-Jul-2026.)
(𝜑 → ∀∃𝑥 ∈ 𝐴(𝜓 → 𝜒))    ⇒   (𝜑 → ∀𝑥 ∈ 𝐴 (𝜓 → 𝜒))
 
12-Jul-2026ralsd 50832 Introduction rule for "all some" restricted to a class. This is the converse of rals1d 50835 and rals2d 50836 taken together. (Contributed by David A. Wheeler, 12-Jul-2026.)
(𝜑 → ∀𝑥 ∈ 𝐴 (𝜓 → 𝜒))    &   (𝜑 → ∃𝑥 ∈ 𝐴 𝜓)    ⇒   (𝜑 → ∀∃𝑥 ∈ 𝐴(𝜓 → 𝜒))
 
12-Jul-2026alsd 50831 Introduction rule: "all some" holds if the "for all" part holds and the antecedent has a witness. This is the converse of als1d 50833 and als2d 50834 taken together, and is what lets an "all some" statement be proved rather than merely taken apart. (Contributed by David A. Wheeler, 12-Jul-2026.)
(𝜑 → ∀𝑥(𝜓 → 𝜒))    &   (𝜑 → ∃𝑥𝜓)    ⇒   (𝜑 → ∀∃𝑥(𝜓 → 𝜒))
 
12-Jul-2026dfrals2 50830 The bounded "all some" form is the general form with the class membership folded into the antecedent. (Contributed by David A. Wheeler, 22-Oct-2018.) (Revised by David A. Wheeler, 12-Jul-2026.)
(∀∃𝑥 ∈ 𝐴(𝜑 → 𝜓) ↔ ∀∃𝑥((𝑥 ∈ 𝐴 ∧ 𝜑) → 𝜓))
 
12-Jul-2026df-rals 50829 Define "all some" applied to a class, which means 𝜓 is true whenever 𝜑 is true for 𝑥 in 𝐴, and there is at least one 𝑥 in 𝐴 where 𝜑 is true.

An older definition of the "all some" quantifier when scoped to a class, named df-alsc and now removed, instead applied a bare formula 𝜑 to the members of a class, asserting only (∀𝑥 ∈ 𝐴𝜑 ∧ ∃𝑥𝑥 ∈ 𝐴), that is, that the formula held throughout 𝐴 and that 𝐴 had at least one member. I've now decided that that was a mistake. Its older existence conjunct ∃𝑥𝑥 ∈ 𝐴 did not require any member of 𝐴 to satisfy the antecedent, so if the formula was itself an implication, that inner implication could still be vacuously true, which is precisely what the allsome quantifier exists to prevent. For example, the older definition meant that "among Martians, all tall ones are green" could be considered true if there are Martians, but no tall Martians. This version of the definition instead ensures that claims of the form "among Martians, all tall ones are green" can only be true if all tall Martians are green and that there is at least one tall Martian. (Contributed by David A. Wheeler, 20-Oct-2018.) (Revised by David A. Wheeler, 12-Jul-2026.)

(∀∃𝑥 ∈ 𝐴(𝜑 → 𝜓) ↔ (∀𝑥 ∈ 𝐴 (𝜑 → 𝜓) ∧ ∃𝑥 ∈ 𝐴 𝜑))
 
12-Jul-2026wrals 50827 Extend wff definition to include "all some" applied to a class, which means 𝜓 is true whenever 𝜑 is true for 𝑥 in 𝐴, and there is at least one 𝑥 in 𝐴 where 𝜑 is true. (Contributed by David A. Wheeler, 20-Oct-2018.) (Revised by David A. Wheeler, 12-Jul-2026.)
wff ∀∃𝑥 ∈ 𝐴(𝜑 → 𝜓)
 
12-Jul-2026wals 50826 Extend wff definition to include "all some" applied to a top-level implication, which means 𝜓 is true whenever 𝜑 is true, and there is at least one 𝑥 where 𝜑 is true. (Contributed by David A. Wheeler, 20-Oct-2018.) (Revised by David A. Wheeler, 12-Jul-2026.)
wff ∀∃𝑥(𝜑 → 𝜓)
 
12-Jul-2026idomnzd 49387 A domain has no zero-divisors (besides zero). (Contributed by Jeff Madsen, 19-Jun-2010.) (Revised by AV, 12-Jul-2026.)
𝐵 = (Base‘𝑅)    &    · = (.r‘𝑅)    &    0 = (0g‘𝑅)    ⇒   ((𝑅 ∈ IDomn ∧ (𝑋 ∈ 𝐵 ∧ 𝑌 ∈ 𝐵 ∧ (𝑋 · 𝑌) = 0 )) → (𝑋 = 0 ∨ 𝑌 = 0 ))
 
12-Jul-2026isidom3 49386 The predicate "is a domain", alternate expression. (Contributed by Jeff Madsen, 19-Jun-2010.) (Revised by AV, 12-Jul-2026.)
𝐵 = (Base‘𝑅)    &    · = (.r‘𝑅)    &    0 = (0g‘𝑅)    &    1 = (1r‘𝑅)    ⇒   (𝑅 ∈ IDomn ↔ (𝑅 ∈ CRing ∧ 0 ≠ 1 ∧ ∀𝑎 ∈ 𝐵 ∀𝑏 ∈ 𝐵 ((𝑎 · 𝑏) = 0 → (𝑎 = 0 ∨ 𝑏 = 0 ))))
 
12-Jul-2026bj-vn0ALT 37955 Alternate proof of vn0 4291 which does not use eqabbw 2834 (and is shorter than vn0 4291 when eqabbw 2834 is inlined). (Contributed by BJ, 12-Jul-2026.) Using the same dummy variable for 𝑦 and 𝑧 slightly reduces the proof size. (Proof modification is discouraged.) (New usage is discouraged.)
V ≠ ∅
 
12-Jul-2026cmprmidlmcl 21611 The complement of a prime ideal is multiplicatively closed. (Contributed by Jeff Madsen, 17-Jun-2011.) (Revised by AV, 12-Jul-2026.)
𝐵 = (Base‘𝑅)    &    · = (.r‘𝑅)    ⇒   (((𝑅 ∈ CRing ∧ 𝑃 ∈ (PrmIdeal‘𝑅)) ∧ (𝐼 ∈ (𝐵 ∖ 𝑃) ∧ 𝐽 ∈ (𝐵 ∖ 𝑃))) → (𝐼 · 𝐽) ∈ (𝐵 ∖ 𝑃))
 
12-Jul-2026prmidlc2 21610 Property of a prime ideal in a commutative ring. (Contributed by Jeff Madsen, 17-Jun-2011.) (Revised by AV, 12-Jul-2026.)
𝐵 = (Base‘𝑅)    &    · = (.r‘𝑅)    ⇒   (((𝑅 ∈ CRing ∧ 𝑃 ∈ (PrmIdeal‘𝑅)) ∧ (𝐼 ∈ (𝐵 ∖ 𝑃) ∧ 𝐽 ∈ 𝐵 ∧ (𝐼 · 𝐽) ∈ 𝑃)) → 𝐽 ∈ 𝑃)
 
12-Jul-2026rspsn0 21506 A principal ideal (an ideal generated by one element) in a ring. (Contributed by Jeff Madsen, 10-Jun-2010.) (Revised by AV, 12-Jul-2026.)
𝐵 = (Base‘𝑅)    &    · = (.r‘𝑅)    &   𝐾 = (RSpan‘𝑅)    ⇒   ((𝑅 ∈ Ring ∧ 𝑋 ∈ 𝐵) → (𝐾‘{𝑋}) = {𝑖 ∈ 𝐵 ∣ ∃𝑥 ∈ 𝐵 𝑖 = (𝑥 · 𝑋)})
 
12-Jul-2026nvpss 4363 No class strictly includes the universal class. Dual of npss0 4361. (Contributed by BJ, 12-Jul-2026.)
¬ V ⊊ 𝐴
 
12-Jul-2026vvin 4359 Two classes are both the universal class if and only if their intersection is the universal class. Dual of un00 4357. (Contributed by BJ, 12-Jul-2026.)
((𝐴 = V ∧ 𝐵 = V) ↔ (𝐴 ∩ 𝐵) = V)
 
12-Jul-2026vn0 4291 The universal class is not equal to the empty set. (Contributed by NM, 11-Sep-2008.) Avoid ax-8 2147, df-clel 2836. (Revised by GG, 6-Sep-2024.) (Proof shortened by BJ, 12-Jul-2026.)
V ≠ ∅
 
10-Jul-202625or6to4 43224 Question 67 of 68 from a lecture Prof. Loof Lirpa held last Saturday in Lincoln Park. When asked why the smaller root wasn't reduced to 3/2, Lirpa responded "It really doesn't matter anyhow." (Contributed by Luke Murphy, 10-Jul-2026.)
(𝜑 → 𝐴 = 1)    &   (𝜑 → 𝐵 = -(53 / 2))    &   (𝜑 → 𝐶 = (75 / 2))    &   (𝜑 → 𝑋 ∈ ℂ)    ⇒   (𝜑 → (((𝐴 · (𝑋↑2)) + ((𝐵 · 𝑋) + 𝐶)) = 0 ↔ (𝑋 = 25 ∨ 𝑋 = (6 / 4))))
 
10-Jul-2026quadfac 43223 The solution of a quadratic equation via factoring. (Contributed by Luke Murphy, 10-Jul-2026.)
(𝜑 → 𝐴 ∈ ℂ)    &   (𝜑 → 𝐴 ≠ 0)    &   (𝜑 → 𝐵 ∈ ℂ)    &   (𝜑 → 𝐶 ∈ ℂ)    &   (𝜑 → 𝑋 ∈ ℂ)    &   (𝜑 → 𝑀 ∈ ℂ)    &   (𝜑 → 𝑁 ∈ ℂ)    &   (𝜑 → (𝑀 + 𝑁) = -(𝐵 / 𝐴))    &   (𝜑 → (𝑀 · 𝑁) = (𝐶 / 𝐴))    ⇒   (𝜑 → (((𝐴 · (𝑋↑2)) + ((𝐵 · 𝑋) + 𝐶)) = 0 ↔ (𝑋 = 𝑀 ∨ 𝑋 = 𝑁)))
 
10-Jul-2026nelscottrankgt 35727 If a member of the input set is not a member of the Scott's trick set, then its rank is greater than the rank of a member of the Scott's trick set. (Contributed by BTernaryTau, 10-Jul-2026.)
((𝐴 ∈ Scott 𝐵 ∧ 𝐶 ∈ 𝐵 ∧ ¬ 𝐶 ∈ Scott 𝐵) → (rank‘𝐴) ∈ (rank‘𝐶))
 
10-Jul-2026scottrankeqel 35726 If a member of the input set has the same rank as a member of the Scott's trick set, then it is also a member of the Scott's trick set. (Contributed by BTernaryTau, 10-Jul-2026.)
((𝐴 ∈ Scott 𝐵 ∧ 𝐶 ∈ 𝐵 ∧ (rank‘𝐶) = (rank‘𝐴)) → 𝐶 ∈ Scott 𝐵)
 
10-Jul-2026elscott2 35722 Membership in a Scott's trick set. (Contributed by BTernaryTau, 10-Jul-2026.)
(𝐴 ∈ Scott 𝐵 ↔ (𝐴 ∈ 𝐵 ∧ (rank‘𝐴) = ∩ (rank “ 𝐵)))
 
10-Jul-2026dfscott3 35721 Alternate definition of a Scott's trick set. (Contributed by BTernaryTau, 10-Jul-2026.)
Scott 𝐴 = (𝐴 ∩ (𝑅1‘suc ∩ (rank “ 𝐴)))
 
10-Jul-2026imadifssran 6195 Condition for the range of a class to be the range of one of its restrictions. (Contributed by AV, 4-Oct-2025.) Remove antecedent. (Revised by Eric Schmidt, 10-Jul-2026.)
((𝐹 “ (dom 𝐹 ∖ 𝐴)) ⊆ ran (𝐹 ↾ 𝐴) → ran 𝐹 = ran (𝐹 ↾ 𝐴))
 
9-Jul-2026elscottrankeq 35724 Elements in a Scott's trick set have the same rank. (Contributed by BTernaryTau, 9-Jul-2026.)
((𝐴 ∈ Scott 𝐶 ∧ 𝐵 ∈ Scott 𝐶) → (rank‘𝐴) = (rank‘𝐵))
 
8-Jul-2026rankscott 35730 The rank of a nonempty Scott's trick set. (Contributed by BTernaryTau, 8-Jul-2026.)
(𝐴 ≠ ∅ → (rank‘Scott 𝐴) = suc ∩ (rank “ 𝐴))
 
8-Jul-2026elscottrank 35723 The rank of an element in a Scott's trick set. (Contributed by BTernaryTau, 8-Jul-2026.)
(𝐴 ∈ Scott 𝐵 → (rank‘𝐴) = ∩ (rank “ 𝐵))
 
8-Jul-2026dfscott2 35720 Alternate definition of a Scott's trick set. (Contributed by BTernaryTau, 8-Jul-2026.)
Scott 𝐴 = {𝑥 ∈ 𝐴 ∣ (rank‘𝑥) = ∩ (rank “ 𝐴)}
 
7-Jul-2026hashomiso 45967 The ♯ function yields an order isomorphism between ω and ℕ0. (Contributed by Eric Schmidt, 7-Jul-2026.)
(♯ ↾ ω) Isom E , < (ω, ℕ0)
 
7-Jul-2026hashomf1o 45966 The ♯ function yields a bijection from ω to ℕ0. (Contributed by Eric Schmidt, 7-Jul-2026.)
(♯ ↾ ω):ω–1-1-onto→ℕ0
 
7-Jul-2026hashnnltb 45965 The ♯ function on ω preserves the ordering. (Contributed by Eric Schmidt, 7-Jul-2026.)
((𝐴 ∈ ω ∧ 𝐵 ∈ ω) → (𝐴 ∈ 𝐵 ↔ (♯‘𝐴) < (♯‘𝐵)))
 
7-Jul-2026hashnnlt 45964 The ♯ function on ω preserves the ordering. (Contributed by Eric Schmidt, 7-Jul-2026.)
((𝐴 ∈ ω ∧ 𝐵 ∈ 𝐴) → (♯‘𝐵) < (♯‘𝐴))
 
7-Jul-2026hashnnm 45963 The ♯ function on ω preserves multiplication. (Contributed by Eric Schmidt, 7-Jul-2026.)
((𝐴 ∈ ω ∧ 𝐵 ∈ ω) → (♯‘(𝐴 ·o 𝐵)) = ((♯‘𝐴) · (♯‘𝐵)))
 
7-Jul-2026hashnnsuc 45962 The ♯ function on ω turns successor into adding 1. (Contributed by Eric Schmidt, 7-Jul-2026.)
(𝐴 ∈ ω → (♯‘suc 𝐴) = ((♯‘𝐴) + 1))
 
7-Jul-2026hashnna 45961 The ♯ function on ω preserves addition. (Contributed by Eric Schmidt, 7-Jul-2026.)
((𝐴 ∈ ω ∧ 𝐵 ∈ ω) → (♯‘(𝐴 +o 𝐵)) = ((♯‘𝐴) + (♯‘𝐵)))
 
7-Jul-2026kardexen 35804 One set is equinumerous to another iff an element in its kard cardinality is equinumerous to an element in the second set's kard cardinality. See kardeng 35798 for a version with equality of cardinals. (Contributed by BTernaryTau, 7-Jul-2026.)
(𝐴 ≈ 𝐵 ↔ ∃𝑥 ∈ (kard‘𝐴)∃𝑦 ∈ (kard‘𝐵)𝑥 ≈ 𝑦)
 
6-Jul-2026kardsdom 35803 One set strictly dominates another iff an element in its kard cardinality strictly dominates an element in the second set's kard cardinality. (Contributed by BTernaryTau, 6-Jul-2026.)
(𝐴 ≺ 𝐵 ↔ ∃𝑥 ∈ (kard‘𝐴)∃𝑦 ∈ (kard‘𝐵)𝑥 ≺ 𝑦)
 
5-Jul-2026prlngeu 29415 Given a line 𝐴 and a point 𝑋 not on 𝐴, a unique line parallel to 𝐴 can be drawn through 𝑋. Theorem 12.13 of [Schwabhauser] p. 124. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ (𝑃 ∖ 𝐴))    &   (𝜑 → 𝐺 ∈ TarskiGE)    ⇒   (𝜑 → ∃!𝑏 ∈ ran 𝐿(𝐴 ∥ 𝑏 ∧ 𝑋 ∈ 𝑏))
 
5-Jul-2026prlngmo 29414 Playfair's axiom. Given a line 𝐴 and a point 𝑋 not on 𝐴, at most one line parallel to 𝐴 can be drawn through 𝑋. Theorem 12.11 of [Schwabhauser] p. 123. Note that this is the first instance of a theorem where the geometry is required to be Euclidean, as expressed by 𝐺 ∈ TarskiGE. Theorem A10 of [Schwabhauser] p. 24 is used, in the form of axtgeucl 28916, in the proof of prlngmolem1 29412. See prlngex 29411 for the corresponding existence theorem. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ (𝑃 ∖ 𝐴))    &   (𝜑 → 𝐺 ∈ TarskiGE)    ⇒   (𝜑 → ∃*𝑏 ∈ ran 𝐿(𝐴 ∥ 𝑏 ∧ 𝑋 ∈ 𝑏))
 
5-Jul-2026prlngmolem2 29413 Lemma for prlngmo 29414. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ (𝑃 ∖ 𝐴))    &   (𝜑 → 𝐺 ∈ TarskiGE)    &   𝑂 = {⟨𝑥, 𝑦⟩ ∣ ((𝑥 ∈ (𝑃 ∖ 𝑏) ∧ 𝑦 ∈ (𝑃 ∖ 𝑏)) ∧ ∃𝑟 ∈ 𝑏 𝑟 ∈ (𝑥(Itv‘𝐺)𝑦))}    &   𝑄 = {⟨𝑥, 𝑦⟩ ∣ ((𝑥 ∈ (𝑃 ∖ 𝐴) ∧ 𝑦 ∈ (𝑃 ∖ 𝐴)) ∧ ∃𝑠 ∈ 𝐴 𝑠 ∈ (𝑥(Itv‘𝐺)𝑦))}    ⇒   (𝜑 → ∃*𝑏 ∈ ran 𝐿(𝐴 ∥ 𝑏 ∧ 𝑋 ∈ 𝑏))
 
5-Jul-2026prlngmolem1 29412 Lemma for prlngmo 29414: Contradiction: Assuming two different parallels 𝐵 and 𝐶 having a common point 𝑋 exist to a line 𝐴, the geometry cannot be Euclidean (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ (𝑃 ∖ 𝐴))    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ 𝐵) ∧ 𝑏 ∈ (𝑃 ∖ 𝐵)) ∧ ∃𝑦 ∈ 𝐵 𝑦 ∈ (𝑎𝐼𝑏))}    &   𝑄 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ 𝐴) ∧ 𝑏 ∈ (𝑃 ∖ 𝐴)) ∧ ∃𝑤 ∈ 𝐴 𝑤 ∈ (𝑎𝐼𝑏))}    &   𝐼 = (Itv‘𝐺)    &   (𝜑 → 𝐵 ∈ ran 𝐿)    &   (𝜑 → 𝐶 ∈ ran 𝐿)    &   (𝜑 → 𝐴 ∥ 𝐵)    &   (𝜑 → 𝐴 ∥ 𝐶)    &   (𝜑 → 𝑋 ∈ 𝐵)    &   (𝜑 → 𝑋 ∈ 𝐶)    &   (𝜑 → 𝑇 ∈ 𝐴)    &   (𝜑 → 𝑊 ∈ (𝐶 ∖ 𝐵))    &   (𝜑 → 𝐵 ≠ 𝐶)    &   (𝜑 → 𝑊𝑂𝑇)    ⇒   (𝜑 → ¬ 𝐺 ∈ TarskiGE)
 
5-Jul-2026prlngex 29411 There exists at least one parallel line 𝑏 to a given line 𝐴 through a given point 𝑋. Theorem 12.10 of [Schwabhauser] p. 122. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ 𝑃)    ⇒   (𝜑 → ∃𝑏 ∈ ran 𝐿(𝐴 ∥ 𝑏 ∧ 𝑋 ∈ 𝑏))
 
5-Jul-2026perpprlng 29410 If two lines 𝐴 and 𝐵 have a common perpendicular 𝐶 and lie in the same plane 𝐻, then they are parallel. Theorem 12.9 of [Schwabhauser] p. 122. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐻 ∈ ran 𝐸)    &   (𝜑 → 𝐴 ⊆ 𝐻)    &   (𝜑 → 𝐵 ⊆ 𝐻)    &   (𝜑 → 𝐶 ⊆ 𝐻)    &   (𝜑 → 𝐴(⟂G‘𝐺)𝐶)    &   (𝜑 → 𝐵(⟂G‘𝐺)𝐶)    ⇒   (𝜑 → 𝐴 ∥ 𝐵)
 
5-Jul-2026prlngpln3 29409 Two parallel lines are on a common plane. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∥ 𝐵)    &   (𝜑 → 𝐴 ≠ 𝐵)    &   (𝜑 → 𝑋 ∈ 𝐵)    ⇒   (𝜑 → 𝐵 ⊆ (𝐴𝐸𝑋))
 
5-Jul-2026prlnghpg 29406 If two lines 𝐴 and 𝐵 are parallel, then any two points 𝑋 and 𝑌 of 𝐵 lie on the same half-plane limited by 𝐴. Theorem 12.6 of [Schwabhauser] p. 122. . (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∥ 𝐵)    &   (𝜑 → 𝐴 ≠ 𝐵)    &   (𝜑 → 𝑋 ∈ 𝐵)    &   (𝜑 → 𝑌 ∈ 𝐵)    ⇒   (𝜑 → 𝑋((hpG‘𝐺)‘𝐴)𝑌)
 
5-Jul-2026prlngpln 29405 Two parallel lines are on a common plane. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ 𝑉)    &   (𝜑 → 𝐴 ∥ 𝐵)    &   (𝜑 → 𝐴 ≠ 𝐵)    ⇒   (𝜑 → ∃ℎ ∈ ran 𝐸(𝐴 ⊆ ℎ ∧ 𝐵 ⊆ ℎ))
 
5-Jul-2026prlngin0 29404 Two parallel lines do not intersect. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ 𝑉)    &   (𝜑 → 𝐴 ∥ 𝐵)    &   (𝜑 → 𝐴 ≠ 𝐵)    ⇒   (𝜑 → (𝐴 ∩ 𝐵) = ∅)
 
5-Jul-2026prlngrcl2 29403 Reverse closure for parallelism. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ 𝑉)    &   (𝜑 → 𝐴 ∥ 𝐵)    ⇒   (𝜑 → 𝐵 ∈ ran 𝐿)
 
5-Jul-2026prlngrcl1 29402 Reverse closure for parallelism. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝐿 = (LineG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ 𝑉)    &   (𝜑 → 𝐴 ∥ 𝐵)    ⇒   (𝜑 → 𝐴 ∈ ran 𝐿)
 
5-Jul-2026perpeq 29330 Uniqueness of the perpendicular to a line 𝐴 within a plane 𝐻 at a point 𝑋. Theorem 11.20 of [Schwabhauser] p. 99. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝐻 ∈ ran 𝐸)    &   (𝜑 → 𝑋 ∈ 𝐴)    &   (𝜑 → 𝐴 ⊆ 𝐻)    &   (𝜑 → 𝑌 ∈ 𝐻)    &   (𝜑 → 𝑍 ∈ 𝐻)    &   (𝜑 → (𝑋𝐿𝑌)(⟂G‘𝐺)𝐴)    &   (𝜑 → (𝑋𝐿𝑍)(⟂G‘𝐺)𝐴)    ⇒   (𝜑 → (𝑋𝐿𝑌) = (𝑋𝐿𝑍))
 
5-Jul-2026perpeqlem 29329 Lemma for perpeq 29330. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝐻 ∈ ran 𝐸)    &   (𝜑 → 𝑋 ∈ 𝐴)    &   (𝜑 → 𝐴 ⊆ 𝐻)    &   (𝜑 → 𝑌 ∈ 𝐻)    &   (𝜑 → 𝑍 ∈ 𝐻)    &   (𝜑 → (𝑋𝐿𝑌)(⟂G‘𝐺)𝐴)    &   (𝜑 → (𝑋𝐿𝑍)(⟂G‘𝐺)𝐴)    &   (𝜑 → 𝑌((hpG‘𝐺)‘𝐴)𝑍)    ⇒   (𝜑 → (𝑋𝐿𝑌) = (𝑋𝐿𝑍))
 
5-Jul-2026ragraghl 29328 Drawing two right angles at a point 𝑋 on the same side of a line (𝑋𝐿𝑌) leads to points 𝑊 and 𝑍 on the same ray from 𝑋. Theorem 11.19 of [Schwabhauser] p. 99. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → ⟨“𝑌𝑋𝑍”⟩ ∈ (∟G‘𝐺))    &   (𝜑 → ⟨“𝑌𝑋𝑊”⟩ ∈ (∟G‘𝐺))    &   (𝜑 → 𝑍((hpG‘𝐺)‘(𝑌𝐿𝑋))𝑊)    ⇒   (𝜑 → 𝑍((hlG‘𝐺)‘𝑋)𝑊)
 
5-Jul-2026ragcgra 29325 Right angles are congruent with each other. Theorem 11.16 of [Schwabhauser] p. 98. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝐴 ∈ 𝑃)    &   (𝜑 → 𝐵 ∈ 𝑃)    &   (𝜑 → 𝐶 ∈ 𝑃)    &   (𝜑 → ⟨“𝑋𝑌𝑍”⟩ ∈ (∟G‘𝐺))    &   (𝜑 → ⟨“𝐴𝐵𝐶”⟩ ∈ (∟G‘𝐺))    &   (𝜑 → 𝐴 ≠ 𝐵)    &   (𝜑 → 𝐵 ≠ 𝐶)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → 𝑌 ≠ 𝑍)    ⇒   (𝜑 → ⟨“𝑋𝑌𝑍”⟩(cgrA‘𝐺)⟨“𝐴𝐵𝐶”⟩)
 
5-Jul-2026nhpmirhp 29258 If a point 𝑍 is on the plane defined by a line 𝐴 and a point 𝑌, but not on the same half-plane as 𝑌, then its mirror point (𝑀‘𝑍) by a point 𝑋 on 𝐴 is on the same half-plane as 𝑌. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝑆 = (pInvG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   𝑀 = (𝑆‘𝑋)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ 𝐴)    &   (𝜑 → 𝑌 ∈ (𝑃 ∖ 𝐴))    &   (𝜑 → 𝑍 ∈ ((𝐴𝐸𝑌) ∖ 𝐴))    &   (𝜑 → ¬ 𝑌((hpG‘𝐺)‘𝐴)𝑍)    ⇒   (𝜑 → 𝑌((hpG‘𝐺)‘𝐴)(𝑀‘𝑍))
 
5-Jul-2026hpgssplng 29256 Any point 𝑋 on a half plane defined by a line 𝐴 and another point 𝑌 is on the plane defined by 𝐴 and 𝑌. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ (𝑃 ∖ 𝐴))    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋((hpG‘𝐺)‘𝐴)𝑌)    ⇒   (𝜑 → 𝑋 ∈ (𝐴𝐸𝑌))
 
5-Jul-2026mirplncl 29255 The mirror of a point with regard to another point is in the same plane as the two points. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   𝑆 = (pInvG‘𝐺)    &   𝑀 = (𝑆‘𝑋)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐻 ∈ ran 𝐸)    &   (𝜑 → 𝑋 ∈ 𝐻)    &   (𝜑 → 𝑌 ∈ 𝐻)    ⇒   (𝜑 → (𝑀‘𝑌) ∈ 𝐻)
 
5-Jul-2026plngmiropp 29254 Given a line 𝐴 and a point 𝑋 not on 𝐴, then a point 𝑌 on the plane defined by 𝐴 and 𝑋 is either opposite to 𝑋, or opposite to the mirror point of 𝑋 by any point 𝑍 of 𝐴. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   𝑆 = (pInvG‘𝐺)    &   𝑀 = (𝑆‘𝑍)    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ 𝐴) ∧ 𝑏 ∈ (𝑃 ∖ 𝐴)) ∧ ∃𝑡 ∈ 𝐴 𝑡 ∈ (𝑎𝐼𝑏))}    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ (𝑃 ∖ 𝐴))    &   (𝜑 → 𝑌 ∈ ((𝐴𝐸𝑋) ∖ 𝐴))    &   (𝜑 → 𝑍 ∈ 𝐴)    ⇒   (𝜑 → (𝑋𝑂𝑌 ∨ (𝑀‘𝑋)𝑂𝑌))
 
5-Jul-2026oppmir 29214 The mirror point with regard to a point 𝑋 on a line 𝐴 lies on the other side of 𝐴. (Contributed by Thierry Arnoux, 5-Jul-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝑆 = (pInvG‘𝐺)    &   𝑀 = (𝑆‘𝑋)    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ 𝐴) ∧ 𝑏 ∈ (𝑃 ∖ 𝐴)) ∧ ∃𝑡 ∈ 𝐴 𝑡 ∈ (𝑎𝐼𝑏))}    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ 𝐴)    &   (𝜑 → 𝑌 ∈ (𝑃 ∖ 𝐴))    &   𝐿 = (LineG‘𝐺)    ⇒   (𝜑 → 𝑌𝑂(𝑀‘𝑌))
 
5-Jul-2026perpin 29182 If two lines 𝐴 and 𝐵 are perpendicular, then they intersect. (Contributed by Thierry Arnoux, 5-Jul-2026.)
(𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴(⟂G‘𝐺)𝐵)    ⇒   (𝜑 → (𝐴 ∩ 𝐵) ≠ ∅)
 
5-Jul-2026ecase33d 1504 Deduction for elimination by cases. (Contributed by Thierry Arnoux, 5-Jul-2026.)
(𝜑 → ¬ 𝜓)    &   (𝜑 → ¬ 𝜒)    &   (𝜑 → (𝜓 ∨ 𝜒 ∨ 𝜃))    ⇒   (𝜑 → 𝜃)
 
5-Jul-20263anasss 1380 Associative law for conjunction applied to antecedent (eliminates syllogism). Converse of 3anassrs 1381. (Contributed by Thierry Arnoux, 5-Jul-2026.)
((((𝜑 ∧ 𝜓) ∧ 𝜒) ∧ 𝜃) → 𝜏)    ⇒   ((𝜑 ∧ (𝜓 ∧ 𝜒 ∧ 𝜃)) → 𝜏)
 
4-Jul-20261enumkard 35813 The Fundamental Theorem of Enumeration (see https://sites.math.rutgers.edu/~zeilberg/mamarim/mamarimPDF/enu.pdf), extended to all sets.

The expression ∪ 𝑥 ∈ 𝐴({𝑥} × 𝐵) can be thought of as expressing an indexed disjoint union ⊔ 𝑥 ∈ 𝐴𝐵 where each 𝐵 has its elements tagged with the set 𝑥 that generated it. See the comment directly before undjudom 10227 for context on disjoint union as a representation of cardinal addition.

This theorem is not limited to numerable sets, but it also does not depend on AC. See 1enumen 35702 for a version that uses equinumerosity , 1enumcard 35703 for a version that uses the card function, and 1enum 35873 for a version that uses an explicit sum of complex number 1s.

(Contributed by BTernaryTau, 4-Jul-2026.)

(𝐴 ∈ V → (kard‘𝐴) = (kard‘∪ 𝑥 ∈ 𝐴 ({𝑥} × 1o)))
 
4-Jul-2026rankkardu 35812 An upper bound on the rank of a kard cardinal. (Contributed by BTernaryTau, 4-Jul-2026.)
(rank‘(kard‘𝐴)) ⊆ suc (rank‘𝐴)
 
4-Jul-2026karddom 35802 One set dominates another iff an element in its kard cardinality dominates an element in the second set's kard cardinality. (Contributed by BTernaryTau, 4-Jul-2026.)
(𝐴 ≼ 𝐵 ↔ ∃𝑥 ∈ (kard‘𝐴)∃𝑦 ∈ (kard‘𝐵)𝑥 ≼ 𝑦)
 
4-Jul-2026kardsn 35801 A singleton has cardinality one. (Contributed by BTernaryTau, 4-Jul-2026.)
(𝐴 ∈ 𝑉 → (kard‘{𝐴}) = (kard‘1o))
 
4-Jul-2026kardenir 35799 If two sets are equinumerous, then their kard cardinal numbers are equal. (Contributed by BTernaryTau, 4-Jul-2026.)
(𝐴 ≈ 𝐵 → (kard‘𝐴) = (kard‘𝐵))
 
4-Jul-2026rankscottu 35731 An upper bound on the rank of a Scott's trick set. (Contributed by BTernaryTau, 4-Jul-2026.)
(𝐴 ∈ 𝐵 → (rank‘Scott 𝐵) ⊆ suc (rank‘𝐴))
 
3-Jul-2026kardfi 35811 The kard cardinal number of a finite set is finite. (Contributed by BTernaryTau, 3-Jul-2026.)
(𝐴 ∈ Fin → (kard‘𝐴) ∈ Fin)
 
3-Jul-2026kardnnfi 35810 The kard cardinal number of a finite ordinal is finite. (Contributed by BTernaryTau, 3-Jul-2026.)
(𝐴 ∈ ω → (kard‘𝐴) ∈ Fin)
 
3-Jul-2026kardcard 35809 Two sets have equal kard cardinalities iff they have equal card cardinalities. This theorem depends on the Axiom of Choice. (Contributed by BTernaryTau, 3-Jul-2026.)
((𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑊) → ((kard‘𝐴) = (kard‘𝐵) ↔ (card‘𝐴) = (card‘𝐵)))
 
3-Jul-2026ackardcard 35808 The Axiom of Choice implies that two sets have equal kard cardinalities iff they have equal card cardinalities. (Contributed by BTernaryTau, 3-Jul-2026.)
(CHOICE → ((𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑊) → ((kard‘𝐴) = (kard‘𝐵) ↔ (card‘𝐴) = (card‘𝐵))))
 
3-Jul-2026kardcard2 35807 Two numerable sets have equal kard cardinalities iff they have equal card cardinalities. This theorem does not depend on the Axiom of Choice. (Contributed by BTernaryTau, 3-Jul-2026.)
((𝐴 ∈ dom card ∧ 𝐵 ∈ dom card) → ((kard‘𝐴) = (kard‘𝐵) ↔ (card‘𝐴) = (card‘𝐵)))
 
3-Jul-2026kardcard2b 35806 If two sets have equal kard cardinalities, then they have equal card cardinalities. This theorem does not depend on the Axiom of Choice. (Contributed by BTernaryTau, 3-Jul-2026.)
((kard‘𝐴) = (kard‘𝐵) → (card‘𝐴) = (card‘𝐵))
 
3-Jul-2026kardcard2a 35805 If two sets have equal nonzero card cardinalities, then they have equal kard cardinalities. This theorem does not depend on the Axiom of Choice. (Contributed by BTernaryTau, 3-Jul-2026.)
(((card‘𝐴) = (card‘𝐵) ∧ (card‘𝐴) ≠ ∅) → (kard‘𝐴) = (kard‘𝐵))
 
3-Jul-2026kard0b 35800 The empty set is the only set with cardinality zero. This is the kard version of cardeq0 10617. (Contributed by BTernaryTau, 3-Jul-2026.)
((kard‘𝐴) = (kard‘∅) ↔ 𝐴 = ∅)
 
3-Jul-2026kardeng 35798 Two sets are equinumerous iff their kard cardinal numbers are equal. Unlike carden 10616, this theorem does not depend on the Axiom of Choice, but it does depend on the Axiom of Regularity and the Axiom of Infinity. (Contributed by BTernaryTau, 3-Jul-2026.)
(𝐴 ∈ 𝑉 → ((kard‘𝐴) = (kard‘𝐵) ↔ 𝐴 ≈ 𝐵))
 
3-Jul-2026kardeq0 35797 Applying kard to a class yields the empty set iff the class is a proper class. (Contributed by BTernaryTau, 3-Jul-2026.)
((kard‘𝐴) = ∅ ↔ ¬ 𝐴 ∈ V)
 
3-Jul-2026elkarden 35796 Any member of the kard cardinal number of a set is equinumerous to the set. Contrast with cardne 10027 for card cardinals. (Contributed by BTernaryTau, 3-Jul-2026.)
(𝐴 ∈ (kard‘𝐵) → 𝐴 ≈ 𝐵)
 
3-Jul-2026kard0 35795 The kard cardinality of the empty set is the singleton of the empty set. (Contributed by BTernaryTau, 3-Jul-2026.)
(kard‘∅) = {∅}
 
3-Jul-2026kardval2 35794 The value of the kard function. This theorem depends on the Axiom of Regularity and the Axiom of Infinity, but it does not depend on the Axiom of Choice. See also kardval 35793. (Contributed by BTernaryTau, 3-Jul-2026.)
(kard‘𝐴) = {𝑥 ∣ (𝑥 ≈ 𝐴 ∧ ∀𝑦(𝑦 ≈ 𝐴 → (rank‘𝑥) ⊆ (rank‘𝑦)))}
 
3-Jul-2026kardval 35793 The value of the kard function. This theorem depends on the Axiom of Regularity and the Axiom of Infinity, but it does not depend on the Axiom of Choice. See also kardval2 35794. (Contributed by BTernaryTau, 3-Jul-2026.)
(kard‘𝐴) = Scott {𝑥 ∣ 𝑥 ≈ 𝐴}
 
3-Jul-2026kardfn 35792 The kard class is a function on the universe. This theorem depends on the Axiom of Regularity and the Axiom of Infinity, but it does not depend on the Axiom of Choice. (Contributed by BTernaryTau, 3-Jul-2026.)
kard Fn V
 
3-Jul-2026acnum 35733 The Axiom of Choice implies that any set is numerable. (Contributed by BTernaryTau, 3-Jul-2026.)
(CHOICE → (𝐴 ∈ 𝑉 → 𝐴 ∈ dom card))
 
3-Jul-2026scottssr1 35732 Relationship between a Scott's trick set and the cumulative hierarchy. (Contributed by BTernaryTau, 3-Jul-2026.)
(𝐴 ∈ 𝐵 → Scott 𝐵 ⊆ (𝑅1‘suc (rank‘𝐴)))
 
3-Jul-2026scott0bOLD 35729 Obsolete version of scott0b 9918 as of 18-Jul-2026. (Contributed by BTernaryTau, 3-Jul-2026.) (Proof modification is discouraged.) (New usage is discouraged.)
(𝐴 = ∅ ↔ Scott 𝐴 = ∅)
 
3-Jul-2026scottsn 35728 Applying Scott's trick to a singleton leaves it unchanged. (Contributed by BTernaryTau, 3-Jul-2026.)
Scott {𝐴} = {𝐴}
 
3-Jul-2026elscottrankss 35725 Relationship between the ranks of an element in a Scott's trick set and an element in the input set. (Contributed by BTernaryTau, 3-Jul-2026.)
((𝐴 ∈ Scott 𝐵 ∧ 𝐶 ∈ 𝐵) → (rank‘𝐴) ⊆ (rank‘𝐶))
 
3-Jul-2026elscott 35719 Membership in a Scott's trick set. (Contributed by BTernaryTau, 3-Jul-2026.)
(𝐴 ∈ Scott 𝐵 ↔ (𝐴 ∈ 𝐵 ∧ ∀𝑥 ∈ 𝐵 (rank‘𝐴) ⊆ (rank‘𝑥)))
 
3-Jul-2026scotteqi 35718 Equality theorem for the Scott operation. Inference form of scotteq 9912. (Contributed by BTernaryTau, 3-Jul-2026.)
𝐴 = 𝐵    ⇒   Scott 𝐴 = Scott 𝐵
 
3-Jul-2026onrankid 35706 The rank of an ordinal number is itself. (Contributed by BTernaryTau, 3-Jul-2026.)
(𝐴 ∈ On ↔ (rank‘𝐴) = 𝐴)
 
3-Jul-2026scott0 9917 Applying Scott's trick to the empty set leaves it unchanged. (Contributed by BTernaryTau, 3-Jul-2026.)
Scott ∅ = ∅
 
2-Jul-2026df-kard 35791 Define the alternative cardinal number function. Under this definition, the cardinal number of a set is the set of all sets equinumerous to it and having the least possible rank. Definition of [Enderton] p. 222. See kardval 35793 for its value. The principal theorem relating this type of cardinality to equinumerosity is kardeng 35798. Our notation is from Enderton and differentiates this function from the standard cardinal size function defined in df-card 10001. (Contributed by BTernaryTau, 2-Jul-2026.)
kard = (𝑥 ∈ V ↦ Scott {𝑦 ∣ 𝑦 ≈ 𝑥})
 
30-Jun-2026isfieldidl2 21521 Determine if a ring is a field based on its ideals. (Contributed by Jeff Madsen, 6-Jan-2011.) (Revised by AV, 30-Jun-2026.)
𝐵 = (Base‘𝑅)    &    0 = (0g‘𝑅)    &   𝐼 = (LIdeal‘𝑅)    ⇒   (𝑅 ∈ Field ↔ (𝑅 ∈ CRing ∧ 𝐵 ≠ { 0 } ∧ 𝐼 = {{ 0 }, 𝐵}))
 
30-Jun-2026isfieldidl 21520 Determine if a ring is a field based on its ideals. (Contributed by Jeff Madsen, 10-Jun-2010.) (Revised by AV, 30-Jun-2026.)
𝐵 = (Base‘𝑅)    &    0 = (0g‘𝑅)    &   𝐼 = (LIdeal‘𝑅)    &    1 = (1r‘𝑅)    ⇒   (𝑅 ∈ Field ↔ (𝑅 ∈ CRing ∧ 0 ≠ 1 ∧ 𝐼 = {{ 0 }, 𝐵}))
 
30-Jun-2026rspprop 21504 Properties of a class to be the ideal generated by a subset of a ring. (Contributed by Jeff Madsen, 10-Jun-2010.) (Revised by AV, 30-Jun-2026.)
𝐵 = (Base‘𝑅)    &   𝐼 = (LIdeal‘𝑅)    &   𝐾 = (RSpan‘𝑅)    ⇒   ((𝑅 ∈ Ring ∧ 𝑆 ⊆ 𝐵) → ((𝐾‘𝑆) = 𝑋 ↔ (𝑋 ∈ 𝐼 ∧ 𝑆 ⊆ 𝑋 ∧ ∀𝑖 ∈ 𝐼 (𝑆 ⊆ 𝑖 → 𝑋 ⊆ 𝑖))))
 
30-Jun-2026rspvalint 21503 The ideal generated by a subset of a ring as intersection of ideals including the subset. (Contributed by Jeff Madsen, 10-Jun-2010.) (Revised by AV, 30-Jun-2026.)
𝐵 = (Base‘𝑅)    &   𝐼 = (LIdeal‘𝑅)    &   𝐾 = (RSpan‘𝑅)    ⇒   ((𝑅 ∈ Ring ∧ 𝑆 ⊆ 𝐵) → (𝐾‘𝑆) = ∩ {𝑡 ∈ 𝐼 ∣ 𝑆 ⊆ 𝑡})
 
28-Jun-2026inlidl 33953 The intersection of two ideals is an ideal. (Contributed by Jeff Madsen, 16-Jun-2011.) (Revised by AV, 28-Jun-2026.)
((𝑅 ∈ Ring ∧ 𝐼 ∈ (LIdeal‘𝑅) ∧ 𝐽 ∈ (LIdeal‘𝑅)) → (𝐼 ∩ 𝐽) ∈ (LIdeal‘𝑅))
 
28-Jun-2026unichnlidl 21496 The union of a nonempty chain of ideals is an ideal. (Contributed by Jeff Madsen, 5-Jan-2011.) (Revised by AV, 28-Jun-2026.)
((𝑅 ∈ Ring ∧ (𝐶 ≠ ∅ ∧ 𝐶 ⊆ (LIdeal‘𝑅) ∧ ∀𝑖 ∈ 𝐶 ∀𝑗 ∈ 𝐶 (𝑖 ⊆ 𝑗 ∨ 𝑗 ⊆ 𝑖))) → ∪ 𝐶 ∈ (LIdeal‘𝑅))
 
28-Jun-2026lidlunin0 21495 The union of a nonempty subset of ideals in a ring is nonempty. (Contributed by AV, 28-Jun-2026.)
((𝑅 ∈ Ring ∧ 𝐶 ≠ ∅ ∧ 𝐶 ⊆ (LIdeal‘𝑅)) → ∪ 𝐶 ≠ ∅)
 
27-Jun-2026isidom2 49385 The predicate "is an integral domain": An integral domain is a commutative prime ring. (Contributed by Jeff Madsen, 10-Jun-2010.) (Revised by AV, 27-Jun-2026.)
(𝑅 ∈ IDomn ↔ (𝑅 ∈ PrmRing ∧ 𝑅 ∈ CRing))
 
27-Jun-2026dfidom2 49384 Alternate definition of the class of integral domains. An integral domain is a commutative prime ring. (Contributed by Jeff Madsen, 10-Jun-2010.) (Revised by AV, 27-Jun-2026.)
IDomn = (PrmRing ∩ CRing)
 
27-Jun-2026crngprmringdom 49383 A commutative ring is a prime ring if and only if it is a domain. (Contributed by AV, 27-Jun-2026.)
(𝑅 ∈ CRing → (𝑅 ∈ PrmRing ↔ 𝑅 ∈ Domn))
 
27-Jun-2026crngprmringidom 49382 A commutative ring is a prime ring if and only if it is an integral domain. (Contributed by AV, 27-Jun-2026.)
(𝑅 ∈ CRing → (𝑅 ∈ PrmRing ↔ 𝑅 ∈ IDomn))
 
27-Jun-2026df2idl2crng 21557 The predicate "is an ideal of the commutative ring 𝑅". (Contributed by Jeff Madsen, 10-Jun-2010.) (Revised by AV, 27-Jun-2026.)
𝑈 = (2Ideal‘𝑅)    &   𝐵 = (Base‘𝑅)    &    · = (.r‘𝑅)    ⇒   (𝑅 ∈ CRing → (𝐼 ∈ 𝑈 ↔ (𝐼 ∈ (SubGrp‘𝑅) ∧ ∀𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐼 (𝑥 · 𝑦) ∈ 𝐼)))
 
27-Jun-2026lidlbasel 21471 An element of an ideal is an element of the ring. (Contributed by Jeff Madsen, 19-Jun-2010.) (Revised by AV, 27-Jun-2026.)
𝐵 = (Base‘𝑊)    &   𝐼 = (LIdeal‘𝑊)    ⇒   ((𝑈 ∈ 𝐼 ∧ 𝑋 ∈ 𝑈) → 𝑋 ∈ 𝐵)
 
27-Jun-20260ring01eqbi2 20763 In a ring, 0 = 1 iff the ring contains only 0. (Contributed by Jeff Madsen, 6-Jan-2011.) (Revised by AV, 27-Jun-2026.)
𝐵 = (Base‘𝑅)    &    0 = (0g‘𝑅)    &    1 = (1r‘𝑅)    ⇒   (𝑅 ∈ Ring → (𝐵 = { 0 } ↔ 1 = 0 ))
 
26-Jun-2026prmrngring 49379 A prime ring is a ring. (Contributed by Jeff Madsen, 10-Jun-2010.) (Revised by AV, 18-Jun-2026.) (Proof shortened by AV, 26-Jun-2026.)
(𝑅 ∈ PrmRing → 𝑅 ∈ Ring)
 
26-Jun-2026prmringnzring 49378 A prime ring is a nonzero ring. (Contributed by AV, 26-Jun-2026.)
(𝑅 ∈ PrmRing → 𝑅 ∈ NzRing)
 
26-Jun-20261enum 35873 The Fundamental Theorem of Enumeration. According to Doron Zeilberger (in https://sites.math.rutgers.edu/~zeilberg/mamarim/mamarimPDF/enu.pdf), this theorem was independently discovered by several anonymous cave-dwellers.

Zeilberger also states that "While this formula is still useful after all these years, enumerating specific finite sets is no longer considered mathematics. A genuine mathematical fact has to incorporate infinitely many facts". Fortunately, theorems in Metamath are actually theorem schemes that correspond to an infinite number of object-language theorems, so this concern does not apply to us.

See 1enumen 35702 for a version that uses equinumerosity , 1enumcard 35703 for a version that uses the card function, and 1enumkard 35813 for a version that uses the kard function.

(Contributed by BTernaryTau, 26-Jun-2026.)

(𝐴 ∈ Fin → (♯‘𝐴) = Σ𝑎 ∈ 𝐴 1)
 
26-Jun-20261enumcard 35703 The Fundamental Theorem of Enumeration (see https://sites.math.rutgers.edu/~zeilberg/mamarim/mamarimPDF/enu.pdf), extended to all sets.

The expression ∪ 𝑥 ∈ 𝐴({𝑥} × 𝐵) can be thought of as expressing an indexed disjoint union ⊔ 𝑥 ∈ 𝐴𝐵 where each 𝐵 has its elements tagged with the set 𝑥 that generated it. See the comment directly before undjudom 10227 for context on disjoint union as a representation of cardinal addition.

This theorem does not depend on AC, but it is only meaningful for numerable sets. See 1enumen 35702 and 1enumkard 35813 for versions that are meaningful for non-numerable sets, and see 1enum 35873 for a version that uses an explicit sum of complex number 1s.

(Contributed by BTernaryTau, 26-Jun-2026.)

(𝐴 ∈ V → (card‘𝐴) = (card‘∪ 𝑥 ∈ 𝐴 ({𝑥} × 1o)))
 
26-Jun-20261enumen 35702 The Fundamental Theorem of Enumeration (see https://sites.math.rutgers.edu/~zeilberg/mamarim/mamarimPDF/enu.pdf), extended to all sets.

The expression ∪ 𝑥 ∈ 𝐴({𝑥} × 𝐵) can be thought of as expressing an indexed disjoint union ⊔ 𝑥 ∈ 𝐴𝐵 where each 𝐵 has its elements tagged with the set 𝑥 that generated it. See the comment directly before undjudom 10227 for context on disjoint union as a representation of cardinal addition.

This theorem is not limited to numerable sets, but it also does not depend on AC. See 1enumcard 35703 for a version that uses the card function, 1enumkard 35813 for a version that uses the kard function , and 1enum 35873 for a version that uses an explicit sum of complex number 1s.

(Contributed by BTernaryTau, 26-Jun-2026.)

(𝐴 ∈ V → 𝐴 ≈ ∪ 𝑥 ∈ 𝐴 ({𝑥} × 1o))
 
26-Jun-20264anpull2 1382 An equivalence of two four-terms conjunctions with the terms regrouped (here, the second sub-conjunct of the first term is pulled separately). (Contributed by Zhi Wang, 4-Sep-2024.) (Proof shortened by Garrett Katz, 26-Jun-2026.)
(((𝜑 ∧ 𝜓) ∧ (𝜒 ∧ 𝜃)) ↔ ((𝜑 ∧ 𝜒 ∧ 𝜃) ∧ 𝜓))
 
25-Jun-2026ifpdfbi 1086 Define the biconditional as conditional logic operator. (Contributed by RP, 20-Apr-2020.) (Proof shortened by Wolf Lammen, 30-Apr-2024.) (Proof shortened by Garrett Katz, 25-Jun-2026.)
((𝜑 ↔ 𝜓) ↔ if-(𝜑, 𝜓, ¬ 𝜓))
 
24-Jun-2026inv2 35692 The intersection of the universal class with a class is itself. A commuted form of inv1 4348. (Contributed by BTernaryTau, 24-Jun-2026.)
(V ∩ 𝐴) = 𝐴
 
23-Jun-2026rankfn 35715 The rank function is a function on the universe. (Contributed by BTernaryTau, 23-Jun-2026.)
rank Fn V
 
23-Jun-2026rankfo 35714 The rank function maps the universe onto the ordinals. (Contributed by BTernaryTau, 23-Jun-2026.)
rank:V–onto→On
 
23-Jun-2026fnfvintima 35695 Condition for a function value to equal the intersection of an image that contains it. (Contributed by BTernaryTau, 23-Jun-2026.)
((𝐹 Fn 𝐴 ∧ 𝐵 ⊆ 𝐴 ∧ 𝐶 ∈ 𝐵) → ((𝐹‘𝐶) = ∩ (𝐹 “ 𝐵) ↔ ∀𝑥 ∈ 𝐵 (𝐹‘𝐶) ⊆ (𝐹‘𝑥)))
 
21-Jun-2026sgnrn 15231 The range of the signum function. (Contributed by AV, 16-Jun-2026.) (Proof shortened by TA, 21-Jun-2026.)
ran sgn = {-1, 0, 1}
 
20-Jun-2026reldmun 6025 Split a relation into two parts based on its domain. (Contributed by Thierry Arnoux, 9-Oct-2023.) Remove requirement that 𝐴 and 𝐵 are disjoint. (Revised by Eric Schmidt, 20-Jun-2026.)
((Rel 𝑅 ∧ dom 𝑅 = (𝐴 ∪ 𝐵)) → 𝑅 = ((𝑅 ↾ 𝐴) ∪ (𝑅 ↾ 𝐵)))
 
19-Jun-2026ringen1zr0 21015 The only unital ring with one element is the zero ring (at least if its operations are internal binary operations). This holds already for nonunital rings, see rngen1zr0 20386, and semirings, see srgen1zr0 20422. (Contributed by FL, 15-Feb-2010.) (Revised by AV, 25-Jan-2020.) (Proof shortened by AV, 19-Jun-2026.)
𝐵 = (Base‘𝑅)    &    + = (+g‘𝑅)    &    ∗ = (.r‘𝑅)    &   𝑍 = (0g‘𝑅)    ⇒   ((𝑅 ∈ Ring ∧ + Fn (𝐵 × 𝐵) ∧ ∗ Fn (𝐵 × 𝐵)) → (𝐵 ≈ 1o ↔ ( + = {⟨⟨𝑍, 𝑍⟩, 𝑍⟩} ∧ ∗ = {⟨⟨𝑍, 𝑍⟩, 𝑍⟩})))
 
19-Jun-2026srg1zr 20421 The only semiring with a base set consisting of one element is the zero ring (at least if its operations are internal binary operations). (Contributed by FL, 13-Feb-2010.) (Revised by AV, 25-Jan-2020.) (Proof shortened by AV, 19-Jun-2026.)
𝐵 = (Base‘𝑅)    &    + = (+g‘𝑅)    &    ∗ = (.r‘𝑅)    ⇒   (((𝑅 ∈ SRing ∧ + Fn (𝐵 × 𝐵) ∧ ∗ Fn (𝐵 × 𝐵)) ∧ 𝑍 ∈ 𝐵) → (𝐵 = {𝑍} ↔ ( + = {⟨⟨𝑍, 𝑍⟩, 𝑍⟩} ∧ ∗ = {⟨⟨𝑍, 𝑍⟩, 𝑍⟩})))
 
18-Jun-2026drngprmrng 49381 A division ring is a prime ring. (Contributed by Jeff Madsen, 6-Jan-2011.) (Revised by AV, 18-Jun-2026.)
(𝑅 ∈ DivRing → 𝑅 ∈ PrmRing)
 
18-Jun-2026smprngprmrng 49380 A simple ring (a nonzero ring whose only ideals are 0 and 𝑅) is a prime ring. (Contributed by Jeff Madsen, 6-Jan-2011.) (Revised by AV, 18-Jun-2026.)
𝐵 = (Base‘𝑅)    &    0 = (0g‘𝑅)    &   𝑈 = (LIdeal‘𝑅)    ⇒   ((𝑅 ∈ NzRing ∧ 𝑈 = {{ 0 }, 𝐵}) → 𝑅 ∈ PrmRing)
 
18-Jun-2026isprmrng 49377 The predicate "is a prime ring". (Contributed by Jeff Madsen, 10-Jun-2010.) (Revised by AV, 18-Jun-2026.)
0 = (0g‘𝑅)    &   𝑃 = (PrmIdeal‘𝑅)    ⇒   (𝑅 ∈ PrmRing ↔ (𝑅 ∈ Ring ∧ { 0 } ∈ 𝑃))
 
18-Jun-2026df-prmring 49376 Define the class of prime rings. A ring is prime if the zero ideal is a prime ideal. (Contributed by Jeff Madsen, 10-Jun-2010.) (Revised by AV, 18-Jun-2026.)
PrmRing = {𝑟 ∈ Ring ∣ {(0g‘𝑟)} ∈ (PrmIdeal‘𝑟)}
 
18-Jun-2026prlngsym 29401 Parallelism is symmetric. Theorem 12.5 of [Schwabhauser] p. 122. (Contributed by Thierry Arnoux, 18-Jun-2026.)
𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ 𝑉)    &   (𝜑 → 𝐴 ∥ 𝐵)    ⇒   (𝜑 → 𝐵 ∥ 𝐴)
 
18-Jun-2026prlngref 29400 Parallelism is reflexive. Theorem 12.4 of [Schwabhauser] p. 122. (Contributed by Thierry Arnoux, 18-Jun-2026.)
𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ 𝑉)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    ⇒   (𝜑 → 𝐴 ∥ 𝐴)
 
18-Jun-2026prlngd 29399 Deduce parallelism between two lines 𝐴 and 𝐵. (Contributed by Thierry Arnoux, 18-Jun-2026.)
𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ 𝑉)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝐵 ∈ ran 𝐿)    &   (𝜑 → 𝐻 ∈ ran 𝐸)    &   (𝜑 → 𝐴 ⊆ 𝐻)    &   (𝜑 → 𝐵 ⊆ 𝐻)    &   (𝜑 → (𝐴 ∩ 𝐵) = ∅)    ⇒   (𝜑 → 𝐴 ∥ 𝐵)
 
18-Jun-2026brprlng 29398 Property of two lines 𝐴 and 𝐵 to be parallel. (Contributed by Thierry Arnoux, 18-Jun-2026.)
𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &    ∥ = (parlnG‘𝐺)    &   (𝜑 → 𝐺 ∈ 𝑉)    ⇒   (𝜑 → (𝐴 ∥ 𝐵 ↔ ((𝐴 ∈ ran 𝐿 ∧ 𝐵 ∈ ran 𝐿) ∧ (𝐴 = 𝐵 ∨ (∃ℎ ∈ ran 𝐸(𝐴 ⊆ ℎ ∧ 𝐵 ⊆ ℎ) ∧ (𝐴 ∩ 𝐵) = ∅)))))
 
18-Jun-2026rngen1zr0 20386 The only ring with one element is the zero ring (at least if its operations are internal binary operations). (Contributed by FL, 15-Feb-2010.) (Revised by AV, 18-Jun-2026.)
𝐵 = (Base‘𝑅)    &    + = (+g‘𝑅)    &    ∗ = (.r‘𝑅)    &    0 = (0g‘𝑅)    ⇒   ((𝑅 ∈ Rng ∧ + Fn (𝐵 × 𝐵) ∧ ∗ Fn (𝐵 × 𝐵)) → (𝐵 ≈ 1o ↔ ( + = {⟨⟨ 0 , 0 ⟩, 0 ⟩} ∧ ∗ = {⟨⟨ 0 , 0 ⟩, 0 ⟩})))
 
18-Jun-2026rngen1zr 20385 The only ring with one element is the zero ring (at least if its operations are internal binary operations). (Contributed by FL, 14-Feb-2010.) (Revised by AV, 18-Jun-2026.)
𝐵 = (Base‘𝑅)    &    + = (+g‘𝑅)    &    ∗ = (.r‘𝑅)    ⇒   (((𝑅 ∈ Rng ∧ + Fn (𝐵 × 𝐵) ∧ ∗ Fn (𝐵 × 𝐵)) ∧ 𝑍 ∈ 𝐵) → (𝐵 ≈ 1o ↔ ( + = {⟨⟨𝑍, 𝑍⟩, 𝑍⟩} ∧ ∗ = {⟨⟨𝑍, 𝑍⟩, 𝑍⟩})))
 
18-Jun-2026rng1zr 20384 The only ring with a base set consisting of one element is the zero ring (at least if its operations are internal binary operations). (Contributed by FL, 13-Feb-2010.) (Revised by AV, 18-Jun-2026.)
𝐵 = (Base‘𝑅)    &    + = (+g‘𝑅)    &    ∗ = (.r‘𝑅)    ⇒   (((𝑅 ∈ Rng ∧ + Fn (𝐵 × 𝐵) ∧ ∗ Fn (𝐵 × 𝐵)) ∧ 𝑍 ∈ 𝐵) → (𝐵 = {𝑍} ↔ ( + = {⟨⟨𝑍, 𝑍⟩, 𝑍⟩} ∧ ∗ = {⟨⟨𝑍, 𝑍⟩, 𝑍⟩})))
 
18-Jun-2026rng1zrlem 20383 Lemma for rng1zr 20384 and srg1zr 20421. (Contributed by FL, 13-Feb-2010.) (Revised by AV, 18-Jun-2026.)
𝐵 = (Base‘𝑅)    &    + = (+g‘𝑅)    &    ∗ = (.r‘𝑅)    ⇒   (((𝑅 ∈ Mgm ∧ (mulGrp‘𝑅) ∈ Mgm) ∧ ( + Fn (𝐵 × 𝐵) ∧ ∗ Fn (𝐵 × 𝐵)) ∧ 𝑍 ∈ 𝐵) → (𝐵 = {𝑍} ↔ ( + = {⟨⟨𝑍, 𝑍⟩, 𝑍⟩} ∧ ∗ = {⟨⟨𝑍, 𝑍⟩, 𝑍⟩})))
 
17-Jun-2026df-prlng 29397 Define the parallel relation for lines. Definition 12.2 of [Schwabhauser] p. 121. Note that the textbook first defines a "strict" parallelism where equal lines are not considered parallel in the strict sense: here we jump directly to the more common definition which allows equality. (Contributed by Thierry Arnoux, 17-Jun-2026.)
parlnG = (𝑔 ∈ V ↦ {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ ran (LineG‘𝑔) ∧ 𝑏 ∈ ran (LineG‘𝑔)) ∧ (𝑎 = 𝑏 ∨ (∃ℎ ∈ ran (hlG‘𝑔)(𝑎 ⊆ ℎ ∧ 𝑏 ⊆ ℎ) ∧ (𝑎 ∩ 𝑏) = ∅)))})
 
17-Jun-2026plng3p 29257 If 𝐻 is a plane containing a line 𝐴 and a point 𝑅 not on 𝐴, then 𝐻 is the plane defined by 𝐴 and 𝑅. Theorem 9.26 of [Schwabhauser] p. 76. See tglinethru 29086 for the 2-point line equivalent. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐻 ∈ ran 𝐸)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑅 ∈ (𝐻 ∖ 𝐴))    &   (𝜑 → 𝐴 ⊆ 𝐻)    ⇒   (𝜑 → 𝐻 = (𝐴𝐸𝑅))
 
17-Jun-2026lnssplng1 29253 A line defined by two points 𝑋 and 𝑌, both on a plane 𝐻, is entirely contained in 𝐻. First part of Theorem 9.25 of [Schwabhauser] p. 75. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐻 ∈ ran 𝐸)    &   (𝜑 → 𝑋 ∈ 𝐻)    &   (𝜑 → 𝑌 ∈ 𝐻)    &   (𝜑 → 𝑋 ≠ 𝑌)    ⇒   (𝜑 → (𝑋𝐿𝑌) ⊆ 𝐻)
 
17-Jun-2026lnssplng 29252 A line defined by two points 𝑋 and 𝑌, both on a plane 𝐻, is entirely contained in 𝐻. Theorem 9.25 of [Schwabhauser] p. 75. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐻 ∈ ran 𝐸)    &   (𝜑 → 𝑋 ∈ 𝐻)    &   (𝜑 → 𝑌 ∈ 𝐻)    &   (𝜑 → 𝑋 ≠ 𝑌)    ⇒   (𝜑 → ((𝑋𝐿𝑌) ⊆ 𝐻 ∧ ∃𝑠 ∈ (𝑃 ∖ (𝑋𝐿𝑌))𝐻 = ((𝑋𝐿𝑌)𝐸𝑠)))
 
17-Jun-2026lnssplnglem 29251 Lemma for lnssplng 29252. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ (𝐴𝐸𝑅))    &   (𝜑 → 𝑌 ∈ (𝐴𝐸𝑅))    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑅 ∈ (𝑃 ∖ 𝐴))    &   (𝜑 → 𝐴 ≠ (𝑋𝐿𝑌))    &   (𝜑 → ¬ 𝑌 ∈ 𝐴)    ⇒   (𝜑 → ((𝑋𝐿𝑌) ⊆ (𝐴𝐸𝑅) ∧ ∃𝑠 ∈ (𝑃 ∖ (𝑋𝐿𝑌))(𝐴𝐸𝑅) = ((𝑋𝐿𝑌)𝐸𝑠)))
 
17-Jun-2026plngrot 29250 The plane defined by a line (𝑋𝐿𝑌) and a point 𝑍 is also defined by the line (𝑍𝐿𝑌) and the point 𝑋. See first part of Theorem 9.24 of [Schwabhauser] p. 74. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ (𝑃 ∖ (𝑍𝐿𝑌)))    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ (𝑃 ∖ (𝑋𝐿𝑌)))    &   (𝜑 → 𝑋 ≠ 𝑌)    ⇒   (𝜑 → ((𝑋𝐿𝑌)𝐸𝑍) = ((𝑍𝐿𝑌)𝐸𝑋))
 
17-Jun-2026plngrotlem3 29249 Lemma for plngrot 29250. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ (𝑃 ∖ (𝑍𝐿𝑌)))    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ (𝑃 ∖ (𝑋𝐿𝑌)))    &   (𝜑 → 𝑋 ≠ 𝑌)    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ (𝑋𝐿𝑌)) ∧ 𝑏 ∈ (𝑃 ∖ (𝑋𝐿𝑌))) ∧ ∃𝑡 ∈ (𝑋𝐿𝑌)𝑡 ∈ (𝑎𝐼𝑏))}    ⇒   (𝜑 → ((𝑋𝐿𝑌)𝐸𝑍) ⊆ ((𝑍𝐿𝑌)𝐸𝑋))
 
17-Jun-2026plngrotlem2 29248 Lemma for plngrot 29250. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ (𝑃 ∖ (𝑍𝐿𝑌)))    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ (𝑃 ∖ (𝑋𝐿𝑌)))    &   (𝜑 → 𝑋 ≠ 𝑌)    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ (𝑋𝐿𝑌)) ∧ 𝑏 ∈ (𝑃 ∖ (𝑋𝐿𝑌))) ∧ ∃𝑡 ∈ (𝑋𝐿𝑌)𝑡 ∈ (𝑎𝐼𝑏))}    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ (𝑍𝐼𝑊))    &   (𝜑 → 𝑌 ≠ 𝑊)    ⇒   (𝜑 → ((𝑋𝐿𝑌)𝐸𝑍) ⊆ ((𝑍𝐿𝑌)𝐸𝑋))
 
17-Jun-2026plngrotlem1 29247 Lemma for plngrot 29250. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ (𝑃 ∖ (𝑍𝐿𝑌)))    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ (𝑃 ∖ (𝑋𝐿𝑌)))    &   (𝜑 → 𝑋 ≠ 𝑌)    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ (𝑋𝐿𝑌)) ∧ 𝑏 ∈ (𝑃 ∖ (𝑋𝐿𝑌))) ∧ ∃𝑡 ∈ (𝑋𝐿𝑌)𝑡 ∈ (𝑎𝐼𝑏))}    &   (𝜑 → 𝑊 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ (𝑍𝐼𝑊))    &   (𝜑 → 𝑌 ≠ 𝑊)    &   (𝜑 → 𝑆 ∈ ((𝑋𝐿𝑌)𝐸𝑍))    &   (𝜑 → (𝑆 ∈ (𝑋𝐿𝑌) ∨ 𝑆((hpG‘𝐺)‘(𝑋𝐿𝑌))𝑍))    ⇒   (𝜑 → 𝑆 ∈ ((𝑍𝐿𝑌)𝐸𝑋))
 
17-Jun-2026plngcp 29246 The plane defined by a line 𝐴 and a point 𝑅 can also be defined using a different point 𝑅 on the same plane: changes the point used to define the plane. Theorem 9.21 of [Schwabhauser] p. 74. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑅 ∈ (𝑃 ∖ 𝐴))    &   (𝜑 → 𝑆 ∈ ((𝐴𝐸𝑅) ∖ 𝐴))    ⇒   (𝜑 → (𝐴𝐸𝑅) = (𝐴𝐸𝑆))
 
17-Jun-2026plngcplem 29245 Lemma for plngcp 29246. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑅 ∈ (𝑃 ∖ 𝐴))    &   (𝜑 → 𝑆 ∈ ((𝐴𝐸𝑅) ∖ 𝐴))    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ 𝐴) ∧ 𝑏 ∈ (𝑃 ∖ 𝐴)) ∧ ∃𝑡 ∈ 𝐴 𝑡 ∈ (𝑎𝐼𝑏))}    ⇒   (𝜑 → (𝐴𝐸𝑅) = (𝐴𝐸𝑆))
 
17-Jun-2026lnincplng 29244 If two lines 𝐴 and 𝐵 intersect, then 𝐵 is in a plane defined by 𝐴 and any point of 𝐵. Lemma 9.22 of [Schwabhauser] p. 74. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝐵 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ 𝐵)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → (𝐴 ∩ 𝐵) = {𝑌})    ⇒   (𝜑 → 𝐵 ⊆ (𝐴𝐸𝑋))
 
17-Jun-2026elplnglnid 29243 The line 𝐴 itself is a subset of a plane defined by the line 𝐴 and a point 𝑅. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑅 ∈ (𝑃 ∖ 𝐴))    ⇒   (𝜑 → 𝐴 ⊆ (𝐴𝐸𝑅))
 
17-Jun-2026elplngid 29242 The point 𝑅 is itself an element of a plane defined by a line 𝐴 and the point 𝑅. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑅 ∈ (𝑃 ∖ 𝐴))    ⇒   (𝜑 → 𝑅 ∈ (𝐴𝐸𝑅))
 
17-Jun-2026plngssp 29241 Planes are sets of points. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑅 ∈ (𝑃 ∖ 𝐴))    &   (𝜑 → 𝑋 ∈ (𝐴𝐸𝑅))    ⇒   (𝜑 → 𝑋 ∈ 𝑃)
 
17-Jun-2026elplng 29240 Elementhood in the plane defined by a line 𝐴 and a point 𝑅. Definition 9.20 of [Schwabhauser] p. 74. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑅 ∈ (𝑃 ∖ 𝐴))    &   𝑂 = {⟨𝑎, 𝑏⟩ ∣ ((𝑎 ∈ (𝑃 ∖ 𝐴) ∧ 𝑏 ∈ (𝑃 ∖ 𝐴)) ∧ ∃𝑡 ∈ 𝐴 𝑡 ∈ (𝑎𝐼𝑏))}    &   (𝜑 → 𝑋 ∈ 𝑃)    ⇒   (𝜑 → (𝑋 ∈ (𝐴𝐸𝑅) ↔ (𝑋 ∈ 𝐴 ∨ 𝑋((hpG‘𝐺)‘𝐴)𝑅 ∨ 𝑋𝑂𝑅)))
 
17-Jun-2026plngrnssp 29239 Planes are sets of points. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐻 ∈ ran 𝐸)    &   (𝜑 → 𝑋 ∈ 𝐻)    ⇒   (𝜑 → 𝑋 ∈ 𝑃)
 
17-Jun-2026isplng 29238 The property of being a plane. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐻 ∈ ran 𝐸)    ⇒   (𝜑 → ∃𝑎 ∈ ran 𝐿∃𝑟 ∈ (𝑃 ∖ 𝑎)𝐻 = (𝑎𝐸𝑟))
 
17-Jun-2026plngval 29237 The plane defined by a line 𝐴 and a point 𝑅 outside of 𝐴. This is defined as the union of 3 parts: the line itself, the open half-plane containing 𝑅, and the points opposite to 𝑅 (see islnopp 29197). (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑅 ∈ (𝑃 ∖ 𝐴))    ⇒   (𝜑 → (𝐴𝐸𝑅) = {𝑥 ∈ 𝑃 ∣ (𝑥 ∈ 𝐴 ∨ 𝑥((hpG‘𝐺)‘𝐴)𝑅 ∨ ∃𝑡 ∈ 𝐴 𝑡 ∈ (𝑥𝐼𝑅))})
 
17-Jun-2026tgelrnpln 29236 The property of being a plane, generated by a line and a point. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ 𝑉)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑅 ∈ (𝑃 ∖ 𝐴))    ⇒   (𝜑 → (𝐴𝐸𝑅) ∈ ran 𝐸)
 
17-Jun-2026tgplnfn 29235 The plane generating function as a function. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   𝐸 = (hlG‘𝐺)    &   (𝜑 → 𝐺 ∈ 𝑉)    ⇒   (𝜑 → 𝐸 Fn ((ran 𝐿 × 𝑃) ∖ ◡ E ))
 
17-Jun-2026df-plng 29234 Define the function building a plane from a line and a point not on that line. Definition 9.20 of [Schwabhauser] p. 74. (Contributed by Thierry Arnoux, 17-Jun-2026.)
hlG = (𝑔 ∈ V ↦ (𝑎 ∈ ran (LineG‘𝑔), 𝑟 ∈ ((Base‘𝑔) ∖ 𝑎) ↦ {𝑥 ∈ (Base‘𝑔) ∣ (𝑥 ∈ 𝑎 ∨ 𝑥((hpG‘𝑔)‘𝑎)𝑟 ∨ ∃𝑡 ∈ 𝑎 𝑡 ∈ (𝑥(Itv‘𝑔)𝑟))}))
 
17-Jun-2026tglnpt4 29105 Find a second point on a line, outside of a second line. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝐵 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ 𝐴)    &   (𝜑 → 𝐴 ≠ 𝐵)    ⇒   (𝜑 → ∃𝑧 ∈ (𝐴 ∖ 𝐵)𝑧 ≠ 𝑋)
 
17-Jun-2026tglnpt3 29104 Find a third point on a line. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝑋 ∈ 𝐴)    &   (𝜑 → 𝑌 ∈ 𝐴)    &   (𝜑 → 𝑋 ≠ 𝑌)    ⇒   (𝜑 → ∃𝑧 ∈ 𝐴 (𝑧 ≠ 𝑋 ∧ 𝑧 ≠ 𝑌))
 
17-Jun-2026tglineinsn 29094 If two distinct lines intersect, it is at a single point. Theorem 6.21 of [Schwabhauser] p. 46. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝐵 ∈ ran 𝐿)    &   (𝜑 → 𝐴 ≠ 𝐵)    &   (𝜑 → 𝑋 ∈ (𝐴 ∩ 𝐵))    ⇒   (𝜑 → (𝐴 ∩ 𝐵) = {𝑋})
 
17-Jun-2026tglinesseq 29090 If a line is a subset of another line, they are equal. (Contributed by Thierry Arnoux, 17-Jun-2026.)
𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ ran 𝐿)    &   (𝜑 → 𝐵 ∈ ran 𝐿)    &   (𝜑 → 𝐴 ⊆ 𝐵)    ⇒   (𝜑 → 𝐴 = 𝐵)
 
17-Jun-2026mpoexd 8082 Existence of an operation class abstraction. (Contributed by Thierry Arnoux, 17-Jun-2026.)
(𝜑 → 𝐴 ∈ 𝑉)    &   ((𝜑 ∧ 𝑥 ∈ 𝐴) → 𝐵 ∈ 𝑊)    ⇒   (𝜑 → (𝑥 ∈ 𝐴, 𝑦 ∈ 𝐵 ↦ 𝐶) ∈ V)
 
17-Jun-2026xpdifcnvepel 6159 The set of couples in a Cartesian product, where the second is not an element of the first. (Contributed by Thierry Arnoux, 17-Jun-2026.)
∪ 𝑥 ∈ 𝐴 ({𝑥} × (𝐵 ∖ 𝑥)) = ((𝐴 × 𝐵) ∖ ◡ E )
 
16-Jun-2026sgnfo 15232 The signum function as onto function. (Contributed by AV, 16-Jun-2026.)
sgn:ℝ*–onto→{-1, 0, 1}
 
16-Jun-2026sgndm 15229 The domain of the signum function. (Contributed by AV, 16-Jun-2026.)
dom sgn = ℝ*
 
16-Jun-2026resdmdfsn 6023 Restricting a class to its domain without a set is the same as restricting the class to the universe without this set. (Contributed by AV, 2-Dec-2018.) Remove antecedent. (Revised by Eric Schmidt, 16-Jun-2026.)
(𝑅 ↾ (V ∖ {𝑋})) = (𝑅 ↾ (dom 𝑅 ∖ {𝑋}))
 
16-Jun-2026resindm 6021 When restricting a class, intersecting with the domain of the class has no effect. (Contributed by FL, 6-Oct-2008.) Remove antecedent. (Revised by Eric Schmidt, 16-Jun-2026.)
(𝐴 ↾ (𝐵 ∩ dom 𝐴)) = (𝐴 ↾ 𝐵)
 
16-Jun-20263jaao 1460 Inference conjoining and disjoining the antecedents of three implications. (Contributed by Jeff Hankins, 15-Aug-2009.) (Proof shortened by Andrew Salmon, 13-May-2011.) (Proof shortened by Garrett Katz, 16-Jun-2026.)
(𝜑 → (𝜓 → 𝜒))    &   (𝜃 → (𝜏 → 𝜒))    &   (𝜂 → (𝜁 → 𝜒))    ⇒   ((𝜑 ∧ 𝜃 ∧ 𝜂) → ((𝜓 ∨ 𝜏 ∨ 𝜁) → 𝜒))
 
16-Jun-20263jaoi 1454 Disjunction of three antecedents (inference). (Contributed by NM, 12-Sep-1995.) (Proof shortened by Garrett Katz, 16-Jun-2026.)
(𝜑 → 𝜓)    &   (𝜒 → 𝜓)    &   (𝜃 → 𝜓)    ⇒   ((𝜑 ∨ 𝜒 ∨ 𝜃) → 𝜓)
 
15-Jun-2026anbiim 653 Adding biconditional when antecedents are conjuncted. (Contributed by metakunt, 16-Apr-2024.) (Proof shortened by Wolf Lammen, 7-May-2025.) (Proof shortened by Garrett Katz, 15-Jun-2026.)
(𝜑 → (𝜒 → 𝜃))    &   (𝜓 → (𝜃 → 𝜒))    ⇒   ((𝜑 ∧ 𝜓) → (𝜒 ↔ 𝜃))
 
15-Jun-2026imbibi 396 The antecedent of one side of a biconditional can be moved out of the biconditional to become the antecedent of the remaining biconditional. (Contributed by BJ, 1-Jan-2025.) (Proof shortened by Wolf Lammen, 5-Jan-2025.) (Proof shortened by Garrett Katz, 15-Jun-2026.)
(((𝜑 → 𝜓) ↔ 𝜒) → (𝜑 → (𝜓 ↔ 𝜒)))
 
13-Jun-2026ad5ant135 1394 Deduction adding conjuncts to antecedent. (Contributed by Alan Sare, 17-Oct-2017.) (Proof shortened by Wolf Lammen, 23-Jun-2022.) (Proof shortened by Garrett Katz, 13-Jun-2026.)
((𝜑 ∧ 𝜓 ∧ 𝜒) → 𝜃)    ⇒   (((((𝜑 ∧ 𝜏) ∧ 𝜓) ∧ 𝜂) ∧ 𝜒) → 𝜃)
 
13-Jun-2026ad5ant134 1392 Deduction adding conjuncts to antecedent. (Contributed by Alan Sare, 17-Oct-2017.) (Proof shortened by Wolf Lammen, 23-Jun-2022.) (Proof shortened by Garrett Katz, 13-Jun-2026.)
((𝜑 ∧ 𝜓 ∧ 𝜒) → 𝜃)    ⇒   (((((𝜑 ∧ 𝜏) ∧ 𝜓) ∧ 𝜒) ∧ 𝜂) → 𝜃)
 
13-Jun-2026ad5ant125 1390 Deduction adding conjuncts to antecedent. (Contributed by Alan Sare, 17-Oct-2017.) (Proof shortened by Wolf Lammen, 23-Jun-2022.) (Proof shortened by Garrett Katz, 13-Jun-2026.)
((𝜑 ∧ 𝜓 ∧ 𝜒) → 𝜃)    ⇒   (((((𝜑 ∧ 𝜓) ∧ 𝜏) ∧ 𝜂) ∧ 𝜒) → 𝜃)
 
13-Jun-2026ad5ant124 1388 Deduction adding conjuncts to antecedent. (Contributed by Alan Sare, 17-Oct-2017.) (Proof shortened by Wolf Lammen, 23-Jun-2022.) (Proof shortened by Garrett Katz, 13-Jun-2026.)
((𝜑 ∧ 𝜓 ∧ 𝜒) → 𝜃)    ⇒   (((((𝜑 ∧ 𝜓) ∧ 𝜏) ∧ 𝜒) ∧ 𝜂) → 𝜃)
 
12-Jun-2026nmulcld 36912 Closure law for natural multiplication. Deduction form. (Contributed by Scott Fenton, 12-Jun-2026.)
(𝜑 → 𝐴 ∈ On)    &   (𝜑 → 𝐵 ∈ On)    ⇒   (𝜑 → (𝐴 ·no 𝐵) ∈ On)
 
12-Jun-2026onvfowev 35868 If 𝐹 maps the ordinals onto the universe, then 𝑅 well-orders the universe. This is the ZFC version of (8 → 3) in https://tinyurl.com/hamkins-gblac. Note that in NBG set theory the antecedent would be something like ∀𝑋(𝑋 ≠ ∅ → ∃𝐹𝐹:On–onto→𝑋), but since we cannot quantify over classes, we instead consider only the case 𝑋 = V which is sufficient for this proof. (Contributed by BTernaryTau, 12-Jun-2026.)
𝑅 = {⟨𝑥, 𝑦⟩ ∣ (𝐻‘𝑥) ∈ (𝐻‘𝑦)}    &   𝐻 = (𝑧 ∈ V ↦ ∩ (◡𝐹 “ {𝑧}))    ⇒   (𝐹:On–onto→V → 𝑅 We V)
 
11-Jun-2026vonf1oonfo 35867 If 𝐹 is a bijection from the ordinals to the universe and 𝐴 is non-empty, then 𝐻 maps the ordinals onto 𝐴. This is the ZFC version of (5 → 8) in https://tinyurl.com/hamkins-gblac, though it neglects to specify that 𝐴 must be non-empty. Note that in NBG set theory the antecedent would be something like ∀𝑋(¬ 𝑋 ∈ V → ∃𝐹𝐹:𝑋–1-1-onto→On), but since we cannot quantify over classes, we instead consider only the case 𝑋 = V which is sufficient for this proof. This theorem can also be viewed as (2 → 8). (Contributed by BTernaryTau, 11-Jun-2026.)
𝐻 = (𝑥 ∈ On ↦ if((𝐹‘𝑥) ∈ 𝐴, (𝐹‘𝑥), 𝐷))    &   𝐷 = (𝐹‘∩ {𝑦 ∈ On ∣ (𝐹‘𝑦) ∈ 𝐴})    ⇒   ((𝐹:On–1-1-onto→V ∧ 𝐴 ≠ ∅) → 𝐻:On–onto→𝐴)
 
11-Jun-2026vonf1owev 35861 If 𝐹 is a bijection from the universe to the ordinals, then 𝑅 well-orders the universe. This is the ZFC version of (2 → 3) in https://tinyurl.com/hamkins-gblac. (Contributed by BTernaryTau, 6-Dec-2025.) (Proof shortened by BTernaryTau, 11-Jun-2026.)
𝑅 = {⟨𝑥, 𝑦⟩ ∣ (𝐹‘𝑥) ∈ (𝐹‘𝑦)}    ⇒   (𝐹:V–1-1-onto→On → 𝑅 We V)
 
11-Jun-2026vonf1wev 35860 If 𝐹 maps the universe one-to-one into the ordinals, then 𝑅 well-orders the universe. This is the ZFC version of (6 → 3) which is used in place of (7 → 3) in https://tinyurl.com/hamkins-gblac. Note that in NBG set theory the antecedent would be something like ∀𝑋∃𝐹𝐹:𝑋–1-1→On, but since we cannot quantify over classes, we instead consider only the case 𝑋 = V which is sufficient for this proof. (Contributed by BTernaryTau, 11-Jun-2026.)
𝑅 = {⟨𝑥, 𝑦⟩ ∣ (𝐹‘𝑥) ∈ (𝐹‘𝑦)}    ⇒   (𝐹:V–1-1→On → 𝑅 We V)
 
10-Jun-2026nmull0 36915 Natural multiplication by zero. (Contributed by Scott Fenton, 10-Jun-2026.)
(𝐴 ∈ On → (∅ ·no 𝐴) = ∅)
 
10-Jun-2026nmulr0 36914 Natural multiplication by zero. (Contributed by Scott Fenton, 10-Jun-2026.)
(𝐴 ∈ On → (𝐴 ·no ∅) = ∅)
 
10-Jun-2026nmulcom 36913 Natural multiplication is commutative. (Contributed by Scott Fenton, 10-Jun-2026.)
((𝐴 ∈ On ∧ 𝐵 ∈ On) → (𝐴 ·no 𝐵) = (𝐵 ·no 𝐴))
 
10-Jun-2026nmulval 36911 Show the value of natural multiplication. (Contributed by Scott Fenton, 10-Jun-2026.)
((𝐴 ∈ On ∧ 𝐵 ∈ On) → (𝐴 ·no 𝐵) = ∩ {𝑥 ∈ On ∣ ∀𝑎 ∈ 𝐴 ∀𝑏 ∈ 𝐵 ((𝑎 ·no 𝐵) +no (𝐴 ·no 𝑏)) ∈ (𝑥 +no (𝑎 ·no 𝑏))})
 
10-Jun-2026nmulcl 36910 Closure law for natural multiplication. (Contributed by Scott Fenton, 10-Jun-2026.)
((𝐴 ∈ On ∧ 𝐵 ∈ On) → (𝐴 ·no 𝐵) ∈ On)
 
10-Jun-2026vonf1oonf1 35866 If 𝐹 is a bijection from the universe to the ordinals, then 𝐻 maps 𝐴 one-to-one into the ordinals. This is the ZFC version of (5 → 6) in https://tinyurl.com/hamkins-gblac. Note that in NBG set theory the antecedent would be something like ∀𝑋(¬ 𝑋 ∈ V → ∃𝐹𝐹:𝑋–1-1-onto→On), but since we cannot quantify over classes, we instead consider only the case 𝑋 = V which is sufficient for this proof. This theorem can also be viewed as (2 → 6). (Contributed by BTernaryTau, 10-Jun-2026.)
𝐻 = (𝐹 ↾ 𝐴)    ⇒   (𝐹:V–1-1-onto→On → 𝐻:𝐴–1-1→On)
 
10-Jun-2026bdaydm 28117 The birthday function's domain is No . (Contributed by Scott Fenton, 14-Jun-2011.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
dom bday = No
 
10-Jun-2026pige0 26770 π is nonnegative. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
0 ≤ π
 
10-Jun-20262picn 26768 (2 · π) is a complex number. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
(2 · π) ∈ ℂ
 
10-Jun-20262pire 26766 (2 · π) is a real number. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
(2 · π) ∈ ℝ
 
10-Jun-202610nprm 17271 10 is not a prime number. (Contributed by Mario Carneiro, 18-Feb-2014.) (Revised by AV, 6-Sep-2021.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
¬ 10 ∈ ℙ
 
10-Jun-20261lt10 12940 1 is less than 10. (Contributed by NM, 7-Nov-2012.) (Revised by Mario Carneiro, 9-Mar-2015.) (Revised by AV, 8-Sep-2021.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
1 < 10
 
10-Jun-20262lt10 12939 2 is less than 10. (Contributed by Mario Carneiro, 10-Mar-2015.) (Revised by AV, 8-Sep-2021.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
2 < 10
 
10-Jun-20263lt10 12938 3 is less than 10. (Contributed by Mario Carneiro, 10-Mar-2015.) (Revised by AV, 8-Sep-2021.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
3 < 10
 
10-Jun-20264lt10 12937 4 is less than 10. (Contributed by Mario Carneiro, 10-Mar-2015.) (Revised by AV, 8-Sep-2021.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
4 < 10
 
10-Jun-20265lt10 12936 5 is less than 10. (Contributed by Mario Carneiro, 10-Mar-2015.) (Revised by AV, 8-Sep-2021.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
5 < 10
 
10-Jun-20266lt10 12935 6 is less than 10. (Contributed by Mario Carneiro, 10-Mar-2015.) (Revised by AV, 8-Sep-2021.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
6 < 10
 
10-Jun-20267lt10 12934 7 is less than 10. (Contributed by Mario Carneiro, 10-Mar-2015.) (Revised by AV, 8-Sep-2021.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
7 < 10
 
10-Jun-20268lt10 12933 8 is less than 10. (Contributed by Mario Carneiro, 8-Feb-2015.) (Revised by AV, 8-Sep-2021.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
8 < 10
 
10-Jun-20269t11e99 12930 9 times 11 equals 99. (Contributed by AV, 14-Jun-2021.) (Revised by AV, 6-Sep-2021.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
(9 · 11) = 99
 
10-Jun-202611nn 12820 11 is a positive integer. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
11 ∈ ℕ
 
10-Jun-202625nn0 12814 25 is a nonnegative integer. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
25 ∈ ℕ0
 
10-Jun-202616nn0 12813 16 is a nonnegative integer. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
16 ∈ ℕ0
 
10-Jun-202612nn0 12812 12 is a nonnegative integer. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
12 ∈ ℕ0
 
10-Jun-202611nn0 12811 11 is a nonnegative integer. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
11 ∈ ℕ0
 
10-Jun-20262le3 12498 2 is less than or equal to 3. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
2 ≤ 3
 
10-Jun-20262t4e8 12493 2 times 4 equals 8. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
(2 · 4) = 8
 
10-Jun-20262t3e6 12490 2 times 3 equals 6. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
(2 · 3) = 6
 
10-Jun-20262m1e1 12448 2 - 1 = 1. The result is on the right-hand-side to be consistent with similar proofs like 4p4e8 12478. (Contributed by David A. Wheeler, 4-Jan-2017.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
(2 − 1) = 1
 
10-Jun-20269pos 12440 The number 9 is positive. (Contributed by NM, 27-May-1999.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
0 < 9
 
10-Jun-20268pos 12439 The number 8 is positive. (Contributed by NM, 27-May-1999.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
0 < 8
 
10-Jun-20267pos 12438 The number 7 is positive. (Contributed by NM, 27-May-1999.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
0 < 7
 
10-Jun-20266pos 12437 The number 6 is positive. (Contributed by NM, 27-May-1999.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
0 < 6
 
10-Jun-20265pos 12436 The number 5 is positive. (Contributed by NM, 27-May-1999.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
0 < 5
 
10-Jun-20264pos 12434 The number 4 is positive. (Contributed by NM, 27-May-1999.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
0 < 4
 
10-Jun-20263pos 12432 The number 3 is positive. (Contributed by NM, 27-May-1999.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
0 < 3
 
10-Jun-20262thalfe1 12431 2 times one half equals 1. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
(2 · (1 / 2)) = 1
 
10-Jun-20262pos 12428 The number 2 is positive. (Contributed by NM, 27-May-1999.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
0 < 2
 
10-Jun-20260le2 12426 The number 0 is less than or equal to 2. (Contributed by David A. Wheeler, 7-Dec-2018.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
0 ≤ 2
 
10-Jun-20261eltp012 12394 1 is an element of {0, 1, 2}. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
1 ∈ {0, 1, 2}
 
10-Jun-20261elpr01 11285 1 is an element of {0, 1}. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
1 ∈ {0, 1}
 
10-Jun-20260elpr01 11282 0 is an element of {0, 1}. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
0 ∈ {0, 1}
 
10-Jun-2026cfon 10313 The cofinality of any set is an ordinal (although it only makes sense when 𝐴 is an ordinal). (Contributed by Mario Carneiro, 9-Mar-2013.) Avoid ax-pow 5327 and ax-un 7740. (Revised by Umit Teoman Dogan, 10-Jun-2026.)
(cf‘𝐴) ∈ On
 
10-Jun-20261n0 8479 Ordinal one is not equal to ordinal zero. (Contributed by NM, 26-Dec-2004.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
1o ≠ ∅
 
10-Jun-20261oelpr 8471 1o is an element of {∅, 1o}. (Contributed by Umit Teoman Dogan, 10-Jun-2026.)
1o ∈ {∅, 1o}
 
10-Jun-2026tfrlem6 8373 Lemma for transfinite recursion. The union of all acceptable functions is a relation. (Contributed by NM, 8-Aug-1994.) (Revised by Mario Carneiro, 9-May-2015.) Avoid ax-10 2178, ax-nul 5260, ax-pr 5391, ax-sep 5249 and ax-un 7740. (Revised by Umit Teoman Dogan, 10-Jun-2026.)
𝐴 = {𝑓 ∣ ∃𝑥 ∈ On (𝑓 Fn 𝑥 ∧ ∀𝑦 ∈ 𝑥 (𝑓‘𝑦) = (𝐹‘(𝑓 ↾ 𝑦)))}    ⇒   Rel recs(𝐹)
 
10-Jun-2026pwuninel 8276 The powerclass of the union of a class does not belong to that class. This theorem provides a way of constructing a new set that does not belong to a given set. See also pwuninel2 8275. (Contributed by NM, 27-Jun-2008.) (Proof shortened by Mario Carneiro, 23-Dec-2016.) Avoid ax-pr 5391 and ax-un 7740. (Revised by Umit Teoman Dogan, 10-Jun-2026.)
¬ 𝒫 ∪ 𝐴 ∈ 𝐴
 
10-Jun-2026peano3 7891 The successor of any natural number is not zero. One of Peano's five postulates for arithmetic. Proposition 7.30(3) of [TakeutiZaring] p. 42. (Contributed by NM, 3-Sep-2003.) Avoid ax-nul 5260. (Revised by Umit Teoman Dogan, 10-Jun-2026.)
(𝐴 ∈ ω → suc 𝐴 ≠ ∅)
 
10-Jun-2026f1odm 6820 The domain of a one-to-one onto mapping. (Contributed by NM, 8-Mar-2014.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
(𝐹:𝐴–1-1-onto→𝐵 → dom 𝐹 = 𝐴)
 
10-Jun-2026f1rel 6774 A one-to-one onto mapping is a relation. (Contributed by NM, 8-Mar-2014.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
(𝐹:𝐴–1-1→𝐵 → Rel 𝐹)
 
10-Jun-2026f1fun 6772 A one-to-one mapping is a function. (Contributed by NM, 8-Mar-2014.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
(𝐹:𝐴–1-1→𝐵 → Fun 𝐹)
 
10-Jun-2026ffun 6704 A mapping is a function. (Contributed by NM, 3-Aug-1994.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
(𝐹:𝐴⟶𝐵 → Fun 𝐹)
 
10-Jun-2026cnvcnvss 6185 The double converse of a class is a subclass. Exercise 2 of [TakeutiZaring] p. 25. (Contributed by NM, 23-Jul-2004.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
◡◡𝐴 ⊆ 𝐴
 
10-Jun-2026rnin 6135 The range of an intersection belongs the intersection of ranges. Theorem 9 of [Suppes] p. 60. (Contributed by NM, 15-Sep-2004.) Avoid ax-pr 5391 and ax-sep 5249. (Revised by Umit Teoman Dogan, 10-Jun-2026.)
ran (𝐴 ∩ 𝐵) ⊆ (ran 𝐴 ∩ ran 𝐵)
 
10-Jun-2026nrelv 5777 The universal class is not a relation. (Contributed by Thierry Arnoux, 23-Jan-2022.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
¬ Rel V
 
10-Jun-2026uniin 4891 The class union of the intersection of two classes. Exercise 4.12(n) of [Mendelson] p. 235. See uniinqs 8802 for a condition where equality holds. (Contributed by NM, 4-Dec-2003.) (Proof shortened by Andrew Salmon, 29-Jun-2011.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
∪ (𝐴 ∩ 𝐵) ⊆ (∪ 𝐴 ∩ ∪ 𝐵)
 
10-Jun-2026pwidg 4577 A set is an element of its power set. (Contributed by Stefan O'Rear, 1-Feb-2015.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
(𝐴 ∈ 𝑉 → 𝐴 ∈ 𝒫 𝐴)
 
10-Jun-2026rab0 4335 Any restricted class abstraction restricted to the empty set is empty. (Contributed by NM, 15-Oct-2003.) (Proof shortened by Andrew Salmon, 26-Jun-2011.) (Proof shortened by JJ, 14-Jul-2021.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
{𝑥 ∈ ∅ ∣ 𝜑} = ∅
 
10-Jun-2026ssinss1 4191 Intersection preserves subclass relationship. (Contributed by NM, 14-Sep-1999.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
(𝐴 ⊆ 𝐶 → (𝐴 ∩ 𝐵) ⊆ 𝐶)
 
10-Jun-2026pssirr 4051 Proper subclass is irreflexive. Theorem 7 of [Suppes] p. 23. (Contributed by NM, 7-Feb-1996.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
¬ 𝐴 ⊊ 𝐴
 
10-Jun-2026nbbn 386 Move negation outside of biconditional. Compare Theorem *5.18 of [WhiteheadRussell] p. 124. (Contributed by NM, 27-Jun-2002.) (Proof shortened by Wolf Lammen, 20-Sep-2013.) (Proof shortened by Umit Teoman Dogan, 10-Jun-2026.)
((¬ 𝜑 ↔ 𝜓) ↔ ¬ (𝜑 ↔ 𝜓))
 
9-Jun-2026wevonprcf1o 35865 If 𝑅 is a set-like well-ordering of the universe and 𝐴 is a proper class, then 𝐹 is a bijection from the ordinals to 𝐴. This is the ZFC version of (4 → 5) in https://tinyurl.com/hamkins-gblac. (Contributed by BTernaryTau, 9-Jun-2026.)
𝐹 = OrdIso(𝑅, 𝐴)    ⇒   ((𝑅 We V ∧ 𝑅 Se V ∧ ¬ 𝐴 ∈ V) → 𝐹:On–1-1-onto→𝐴)
 
9-Jun-2026ordtypeon 35698 A proper class with a set-like well-ordering is isomorphic to the proper class of all ordinal numbers. (Contributed by BTernaryTau, 9-Jun-2026.)
𝐹 = OrdIso(𝑅, 𝐴)    ⇒   ((𝑅 We 𝐴 ∧ 𝑅 Se 𝐴 ∧ ¬ 𝐴 ∈ V) → 𝐹 Isom E , 𝑅 (On, 𝐴))
 
9-Jun-2026ordprcon 35696 If an ordinal class is not a set, then it must be the proper class of all ordinals. (Contributed by BTernaryTau, 9-Jun-2026.)
((Ord 𝐴 ∧ ¬ 𝐴 ∈ V) → 𝐴 = On)
 
8-Jun-2026vonf1osev 35864 If 𝐹 is a bijection from the universe to the ordinals, then 𝑅 is a set-like well-ordering of the universe. This is the ZFC version of (2 → 4) which is used in place of (3 → 4) in https://tinyurl.com/hamkins-gblac. This proof takes advantage of the fact that the well-order constructed in (2 → 3) is also set-like. (Contributed by BTernaryTau, 8-Jun-2026.)
𝑅 = {⟨𝑥, 𝑦⟩ ∣ (𝐹‘𝑥) ∈ (𝐹‘𝑦)}    ⇒   (𝐹:V–1-1-onto→On → (𝑅 We V ∧ 𝑅 Se V))
 
7-Jun-2026pm2.65i 196 Inference for proof by contradiction. (Contributed by NM, 18-May-1994.) (Proof shortened by Wolf Lammen, 11-Sep-2013.) (Proof shortened by Garrett Katz, 7-Jun-2026.)
(𝜑 → 𝜓)    &   (𝜑 → ¬ 𝜓)    ⇒    ¬ 𝜑
 
6-Jun-2026rlocisunit 33819 Characterize the units of the localization 𝐿 of a ring 𝑅 at 𝑆 as the elements with a "numerator" 𝑃 in the saturation 𝑇 of 𝑆. (Contributed by Thierry Arnoux, 6-Jun-2026.)
𝐵 = (Base‘𝑅)    &    · = (.r‘𝑅)    &   𝐿 = (𝑅 RLocal 𝑆)    &   𝑊 = (Unit‘𝐿)    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝑆 ∈ (SubMnd‘(mulGrp‘𝑅)))    &    ∼ = (𝑅 ~RL 𝑆)    &   (𝜑 → 𝑃 ∈ 𝐵)    &   (𝜑 → 𝑄 ∈ 𝑆)    &   𝑇 = {𝑟 ∈ 𝐵 ∣ ∃𝑠 ∈ 𝐵 (𝑟 · 𝑠) ∈ 𝑆}    ⇒   (𝜑 → ([⟨𝑃, 𝑄⟩] ∼ ∈ 𝑊 ↔ 𝑃 ∈ 𝑇))
 
6-Jun-2026rlocinvunit 33818 In the localization of a ring 𝑅 at 𝑆, inverses of elements of 𝑆 are units. (Contributed by Thierry Arnoux, 6-Jun-2026.)
𝐵 = (Base‘𝑅)    &    1 = (1r‘𝑅)    &    ∼ = (𝑅 ~RL 𝑆)    &   𝐿 = (𝑅 RLocal 𝑆)    &   𝑊 = (Unit‘𝐿)    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝑆 ∈ (SubMnd‘(mulGrp‘𝑅)))    &   (𝜑 → 𝑄 ∈ 𝑆)    ⇒   (𝜑 → [⟨ 1 , 𝑄⟩] ∼ ∈ 𝑊)
 
6-Jun-2026isunitc 33784 Characterize units in a commutative ring. (Contributed by Thierry Arnoux, 6-Jun-2026.)
𝐵 = (Base‘𝑅)    &   𝑈 = (Unit‘𝑅)    &    · = (.r‘𝑅)    &    1 = (1r‘𝑅)    &   (𝜑 → 𝑋 ∈ 𝐵)    &   (𝜑 → 𝑅 ∈ CRing)    ⇒   (𝜑 → (𝑋 ∈ 𝑈 ↔ ∃𝑦 ∈ 𝐵 (𝑋 · 𝑦) = 1 ))
 
6-Jun-2026prmidlsubm 21623 The complement of a prime ideal is multiplicatively closed. Converse of ssdifidlprm 21622. (Contributed by Thierry Arnoux, 6-Jun-2026.)
𝐵 = (Base‘𝑅)    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝑃 ∈ (PrmIdeal‘𝑅))    ⇒   (𝜑 → (𝐵 ∖ 𝑃) ∈ (SubMnd‘(mulGrp‘𝑅)))
 
6-Jun-2026prmidlprop 21612 Property of prime ideals. (Contributed by Thierry Arnoux, 6-Jun-2026.)
𝐵 = (Base‘𝑅)    &    · = (.r‘𝑅)    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝑃 ∈ (PrmIdeal‘𝑅))    &   (𝜑 → 𝑋 ∈ 𝐵)    &   (𝜑 → 𝑌 ∈ 𝐵)    &   (𝜑 → (𝑋 · 𝑌) ∈ 𝑃)    ⇒   (𝜑 → (𝑋 ∈ 𝑃 ∨ 𝑌 ∈ 𝑃))
 
5-Jun-2026sbrimvw 2128 Substitution in an implication with a variable not free in the antecedent affects only the consequent. Version of sbrim 2338 based on fewer axioms, but with more disjoint variable conditions. (Contributed by Wolf Lammen, 29-Jan-2024.) Remove DV condition. (Revised by Wolf Lammen, 5-Jun-2026.)
([𝑦 / 𝑥](𝜑 → 𝜓) ↔ (𝜑 → [𝑦 / 𝑥]𝜓))
 
4-Jun-2026morleylemrneab 35283 Lemma for morley . (Contributed by TA and SS, 4-Jun-2026.)
𝑆 = (Base‘𝐺)    &   𝐿 = (LineG‘𝐺)    &    ∼ = (cgrA‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ 𝑆)    &   (𝜑 → 𝐵 ∈ 𝑆)    &   (𝜑 → 𝐶 ∈ 𝑆)    &   (𝜑 → 𝑃 ∈ 𝑆)    &   (𝜑 → 𝑄 ∈ 𝑆)    &   (𝜑 → 𝑅 ∈ 𝑆)    &   (𝜑 → ¬ (𝐶 ∈ (𝐴𝐿𝐵) ∨ 𝐴 = 𝐵))    &   (𝜑 → ⟨“𝐶𝐴𝑄”⟩ ∼ ⟨“𝑄𝐴𝑅”⟩)    &   (𝜑 → ⟨“𝑅𝐴𝐵”⟩ ∼ ⟨“𝑄𝐴𝑅”⟩)    &   (𝜑 → ⟨“𝐴𝐵𝑅”⟩ ∼ ⟨“𝑅𝐵𝑃”⟩)    &   (𝜑 → ⟨“𝑃𝐵𝐶”⟩ ∼ ⟨“𝑅𝐵𝑃”⟩)    &   (𝜑 → ⟨“𝐵𝐶𝑃”⟩ ∼ ⟨“𝑃𝐶𝑄”⟩)    &   (𝜑 → ⟨“𝑄𝐶𝐴”⟩ ∼ ⟨“𝑃𝐶𝑄”⟩)    ⇒   (𝜑 → ¬ 𝑅 ∈ (𝐴𝐿𝐵))
 
4-Jun-2026btwnlng13 35282 If 𝑍 is between 𝑋 and 𝑌, or 𝑌 is between 𝑋 and 𝑍, then 𝑍 lies on the line 𝑋𝑌. (Contributed by SS, 4-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   𝐿 = (LineG‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝑋 ∈ 𝑃)    &   (𝜑 → 𝑌 ∈ 𝑃)    &   (𝜑 → 𝑍 ∈ 𝑃)    &   (𝜑 → 𝑋 ≠ 𝑌)    &   (𝜑 → (𝑍 ∈ (𝑋𝐼𝑌) ∨ 𝑌 ∈ (𝑋𝐼𝑍)))    ⇒   (𝜑 → 𝑍 ∈ (𝑋𝐿𝑌))
 
4-Jun-2026cgranbtwn 35281 Null angle implies betweenness. (Contributed by SS, 4-Jun-2026.)
𝑃 = (Base‘𝐺)    &   𝐼 = (Itv‘𝐺)    &   (𝜑 → 𝐺 ∈ TarskiG)    &   (𝜑 → 𝐴 ∈ 𝑃)    &   (𝜑 → 𝐵 ∈ 𝑃)    &   (𝜑 → 𝐶 ∈ 𝑃)    &   (𝜑 → 𝐷 ∈ 𝑃)    &   (𝜑 → 𝐸 ∈ 𝑃)    &   (𝜑 → 𝐹 ∈ 𝑃)    &   (𝜑 → ⟨“𝐴𝐵𝐶”⟩(cgrA‘𝐺)⟨“𝐷𝐸𝐹”⟩)    &   (𝜑 → 𝐴 ∈ (𝐵𝐼𝐶))    ⇒   (𝜑 → (𝐷 ∈ (𝐸𝐼𝐹) ∨ 𝐹 ∈ (𝐸𝐼𝐷)))
 
4-Jun-2026csbcnv 5864 Move class substitution in and out of the converse of a relation. (Contributed by Thierry Arnoux, 8-Feb-2017.) (Revised by NM, 23-Aug-2018.) Remove dependency on ax-sep 5249 and ax-pr 5391. (Revised by Eric Schmidt, 4-Jun-2026.)
◡⦋𝐴 / 𝑥⦌𝐹 = ⦋𝐴 / 𝑥⦌◡𝐹
 
4-Jun-2026abab 840 Introduce one conjunct as equivalent to the other. "abab" stands for "and, biconditional, and, biconditional". (Contributed by Wolf Lammen, 4-Jun-2026.)
((𝜑 ∧ 𝜓) ↔ (𝜑 ∧ (𝜑 ↔ 𝜓)))
 
3-Jun-2026fldlring 34013 A field is a local ring. (Contributed by Thierry Arnoux, 3-Jun-2026.) (Proof modification is discouraged.)
(𝜑 → 𝐹 ∈ Field)    ⇒   (𝜑 → 𝐹 ∈ LRing)
 
2-Jun-2026nmulprop 36909 Show closure and value of natural multiplication. (Contributed by Scott Fenton, 2-Jun-2026.)
((𝐴 ∈ On ∧ 𝐵 ∈ On) → ((𝐴 ·no 𝐵) ∈ On ∧ (𝐴 ·no 𝐵) = ∩ {𝑥 ∈ On ∣ ∀𝑎 ∈ 𝐴 ∀𝑏 ∈ 𝐵 ((𝑎 ·no 𝐵) +no (𝐴 ·no 𝑏)) ∈ (𝑥 +no (𝑎 ·no 𝑏))}))
 
2-Jun-2026nmulfn 36908 Natural multiplication is a function over pairs of ordinals. (Contributed by Scott Fenton, 2-Jun-2026.)
·no Fn (On × On)
 
2-Jun-2026df-nmul 36907 Define natural ordinal multiplication. This is the corresponding operation to df-nadd 8659. (Contributed by Scott Fenton, 2-Jun-2026.)
·no = frecs({⟨𝑥, 𝑦⟩ ∣ (𝑥 ∈ (On × On) ∧ 𝑦 ∈ (On × On) ∧ (((1st ‘𝑥) E (1st ‘𝑦) ∨ (1st ‘𝑥) = (1st ‘𝑦)) ∧ ((2nd ‘𝑥) E (2nd ‘𝑦) ∨ (2nd ‘𝑥) = (2nd ‘𝑦)) ∧ 𝑥 ≠ 𝑦))}, (On × On), (𝑝 ∈ V, 𝑚 ∈ V ↦ ⦋(1st ‘𝑝) / 𝑎⦌⦋(2nd ‘𝑝) / 𝑏⦌∩ {𝑧 ∈ On ∣ ∀𝑐 ∈ 𝑎 ∀𝑑 ∈ 𝑏 ((𝑐𝑚𝑏) +no (𝑎𝑚𝑑)) ∈ (𝑧 +no (𝑐𝑚𝑑))}))
 
2-Jun-2026dflring4 34012 Alternate definition of a local ring: the set (𝐵 ∖ 𝑈) of non-units is an ideal. (Contributed by Thierry Arnoux, 2-Jun-2026.)
𝐵 = (Base‘𝑅)    &   𝑈 = (Unit‘𝑅)    ⇒   (𝑅 ∈ CRing → (𝑅 ∈ LRing ↔ (𝐵 ∖ 𝑈) ∈ (LIdeal‘𝑅)))
 
2-Jun-2026dflring3 34011 Alternate definition of a local ring: local rings have a single maximal ideal. (Contributed by Thierry Arnoux, 2-Jun-2026.)
(𝑅 ∈ CRing → (𝑅 ∈ LRing ↔ (MaxIdeal‘𝑅) ≈ 1o))
 
2-Jun-2026dflringlem3 34010 Lemma for dflring3 34011. In a commutative local ring 𝑅, the set (𝐵 ∖ 𝑈) of non-units is a maximal ideal. (Contributed by Thierry Arnoux, 2-Jun-2026.)
𝐵 = (Base‘𝑅)    &   𝑈 = (Unit‘𝑅)    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝑅 ∈ LRing)    ⇒   (𝜑 → (𝐵 ∖ 𝑈) ∈ (MaxIdeal‘𝑅))
 
2-Jun-2026dflringlem2 34009 Lemma for dflring3 34011. In a commutative local ring 𝑅, the set (𝐵 ∖ 𝑈) of non-units is an ideal. (Contributed by Thierry Arnoux, 2-Jun-2026.)
𝐵 = (Base‘𝑅)    &   𝑈 = (Unit‘𝑅)    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝑅 ∈ LRing)    ⇒   (𝜑 → (𝐵 ∖ 𝑈) ∈ (LIdeal‘𝑅))
 
2-Jun-2026dflringlem 34008 Lemma for dflring3 34011. If a ring 𝑅 has a single maximal ideal 𝑀, then any element 𝑋 outside of 𝑀 is a unit. (Contributed by Thierry Arnoux, 2-Jun-2026.)
𝐵 = (Base‘𝑅)    &   𝑈 = (Unit‘𝑅)    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝑀 ∈ (MaxIdeal‘𝑅))    &   (𝜑 → (MaxIdeal‘𝑅) = {𝑀})    &   (𝜑 → 𝑋 ∈ (𝐵 ∖ 𝑀))    ⇒   (𝜑 → 𝑋 ∈ 𝑈)
 
2-Jun-2026dflring2 34007 Alternate definition of a local ring. (Contributed by Thierry Arnoux, 2-Jun-2026.)
𝐵 = (Base‘𝑅)    &   𝑈 = (Unit‘𝑅)    &    1 = (1r‘𝑅)    &    − = (-g‘𝑅)    ⇒   (𝑅 ∈ LRing ↔ (𝑅 ∈ NzRing ∧ ∀𝑥 ∈ 𝐵 (𝑥 ∈ 𝑈 ∨ ( 1 − 𝑥) ∈ 𝑈)))
 
2-Jun-2026drnglring 34006 A division ring is a local ring. (Contributed by Thierry Arnoux, 2-Jun-2026.)
(𝜑 → 𝐹 ∈ DivRing)    ⇒   (𝜑 → 𝐹 ∈ LRing)
 
26-May-2026axpowg3 35789 A generalization of ax-pow 5327 that combines axpowg 35787 and axpowg2 35788 into a single theorem scheme. Unlike ax-pow 5327, this scheme lacks a distinct variable condition for 𝑦 and 𝑤 as well as for 𝑥 and 𝑤. Usage of this theorem is discouraged because it depends on ax-13 2402. (Contributed by BTernaryTau, 26-May-2026.) (New usage is discouraged.)
∃𝑦∀𝑧(∀𝑤(𝑤 ∈ 𝑧 → 𝑤 ∈ 𝑥) → 𝑧 ∈ 𝑦)
 
26-May-2026axpowg2 35788 A generalization of ax-pow 5327 in which 𝑥 and 𝑤 need not be distinct. This theorem scheme bundles ax-pow 5327 with the degenerate instance ∃𝑦∀𝑧(∀𝑥(𝑥 ∈ 𝑧 → 𝑥 ∈ 𝑥) → 𝑧 ∈ 𝑦) which is satisfied by the existence of a set that contains all empty sets (see axprlem1 5385). Usage of this theorem is discouraged because it depends on ax-13 2402. (Contributed by BTernaryTau, 26-May-2026.) (New usage is discouraged.)
∃𝑦∀𝑧(∀𝑤(𝑤 ∈ 𝑧 → 𝑤 ∈ 𝑥) → 𝑧 ∈ 𝑦)
 
26-May-2026axpowg 35787 A generalization of ax-pow 5327 that combines it and zfpow 5328 into a single theorem scheme. Unlike ax-pow 5327, this scheme lacks a distinct variable condition for 𝑦 and 𝑤. (Contributed by BTernaryTau, 26-May-2026.)
∃𝑦∀𝑧(∀𝑤(𝑤 ∈ 𝑧 → 𝑤 ∈ 𝑥) → 𝑧 ∈ 𝑦)
 
25-May-2026expt 178 Exportation theorem pm3.3 454 (closed form of ex 418) expressed with primitive connectives. (Contributed by NM, 28-Dec-1992.) (Proof shortened by Garrett Katz, 25-May-2026.)
((¬ (𝜑 → ¬ 𝜓) → 𝜒) → (𝜑 → (𝜓 → 𝜒)))
 
24-May-2026axsepg5 35785 A generalization of ax-sep 5249 that combines axsepg 5250, axsepg2 35781, and axsepg3 35782 into a single theorem scheme. Unlike ax-sep 5249, this scheme lacks a distinct variable condition for 𝜑 and 𝑧, for 𝑥 and 𝑧, and for 𝑦 and 𝑧. Usage of this theorem is discouraged because it depends on ax-13 2402. (Contributed by BTernaryTau, 24-May-2026.) (New usage is discouraged.)
∃𝑦∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))
 
24-May-2026axsepg4 35784 A generalization of ax-sep 5249 that combines axsepg 5250 and axsepg2 35781 into a single theorem scheme. Unlike ax-sep 5249, this scheme lacks a distinct variable condition for 𝜑 and 𝑧 as well as for 𝑥 and 𝑧. Usage of this theorem is discouraged because it depends on ax-13 2402. (Contributed by BTernaryTau, 24-May-2026.) (New usage is discouraged.)
∃𝑦∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))
 
23-May-2026elirrv 9575 The membership relation is irreflexive: no set is a member of itself. Theorem 105 of [Suppes] p. 54. This is trivial to prove from zfregfr 9589 and efrirr 5631 (see elirrvALT 9590), but this proof is direct from ax-reg 9570. (Contributed by NM, 19-Aug-1993.) Reduce axiom dependencies and make use of ax-reg 9570 directly. (Revised by BTernaryTau, 27-Dec-2025.) Avoid ax-pr 5391. (Revised by BTernaryTau, 21-May-2026.) (Proof shortened by Matthew House, 23-May-2026.)
¬ 𝑥 ∈ 𝑥
 
22-May-2026bilanri 512 Inference adding a conjunct to the right-hand side of a biconditional. (Contributed by Matthew House, 22-May-2026.)
(𝜑 ↔ 𝜓)    ⇒   ((𝜒 ∧ 𝜓) → 𝜑)
 
22-May-2026biranri 511 Inference adding a conjunct to the right-hand side of a biconditional. (Contributed by Matthew House, 22-May-2026.)
(𝜑 ↔ 𝜓)    ⇒   ((𝜓 ∧ 𝜒) → 𝜑)
 
22-May-2026bilani 510 Inference adding a conjunct to the left-hand side of a biconditional. (Contributed by Matthew House, 22-May-2026.)
(𝜑 ↔ 𝜓)    ⇒   ((𝜒 ∧ 𝜑) → 𝜓)
 
22-May-2026birani 509 Inference adding a conjunct to the left-hand side of a biconditional. (Contributed by Matthew House, 22-May-2026.)
(𝜑 ↔ 𝜓)    ⇒   ((𝜑 ∧ 𝜒) → 𝜓)
 
21-May-2026axsepg2 35781 A generalization of ax-sep 5249 in which 𝑥 and 𝑧 need not be distinct. This theorem scheme bundles ax-sep 5249 with the degenerate instance ∃𝑦∀𝑧(𝑧 ∈ 𝑦 ↔ (𝑧 ∈ 𝑧 ∧ 𝜑)) which is satisfied by the existence of the empty set. Usage of this theorem is discouraged because it depends on ax-13 2402. (Contributed by BTernaryTau, 21-May-2026.) (New usage is discouraged.)
∃𝑦∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))
 
9-May-2026goldratmolem2 47877 Lemma 2 for determining the value of golden ratio. (Contributed by Ender Ting, 9-May-2026.)
𝐹 = (2 · (cos‘(π / 5)))    ⇒   -1 = ((((𝐹↑5) / 2) − (5 · ((𝐹↑3) / 2))) + (5 · (𝐹 / 2)))
 
9-May-2026goldracos5teq 47876 Lemma 1 for determining the value of golden ratio. (Contributed by Ender Ting, 9-May-2026.)
𝐹 = (2 · (cos‘(π / 5)))    ⇒   (cos‘π) = (((16 · ((𝐹 / 2)↑5)) − (20 · ((𝐹 / 2)↑3))) + (5 · (𝐹 / 2)))
 
9-May-2026cos5teq 47870 Five-times-angle formula for cosine, substitution helper. (Contributed by Ender Ting, 9-May-2026.)
((𝐴 ∈ ℂ ∧ 𝐵 = (5 · 𝐴) ∧ 𝐶 = (cos‘𝐴)) → (cos‘𝐵) = (((16 · (𝐶↑5)) − (20 · (𝐶↑3))) + (5 · 𝐶)))
 
9-May-2026quantgodel 47828 There can be no formula asserting its own non-universality, in parallel to bj-babygodel 37443; proof path is shorter but relying on a property of specialization which provability predicates do not have. For a matching proof, see quantgodelALT 47829. (Contributed by Ender Ting, 9-May-2026.)
(𝜑 ↔ ¬ ∀𝑥𝜑)    ⇒   ⊥
 
9-May-2026funopsn 7143 If a function is an ordered pair then it is a singleton of an ordered pair. (Contributed by AV, 20-Sep-2020.) (Proof shortened by AV, 15-Jul-2021.) (Proof shortened by Eric Schmidt, 9-May-2026.) A function is a class of ordered pairs, so the fact that an ordered pair may sometimes be itself a function is an "accident" depending on the specific encoding of ordered pairs as classes (in set.mm, the Kuratowski encoding). A more meaningful statement is funsng 6583, as relsnopg 5781 is to relop 5828. (New usage is discouraged.)
𝑋 ∈ V    &   𝑌 ∈ V    ⇒   ((Fun 𝐹 ∧ 𝐹 = ⟨𝑋, 𝑌⟩) → ∃𝑎(𝑋 = {𝑎} ∧ 𝐹 = {⟨𝑎, 𝑎⟩}))
 
9-May-2026iunopeqop 5494 Implication of an ordered pair being equal to an indexed union of singletons of ordered pairs. (Contributed by AV, 20-Sep-2020.) Remove antecedent. (Revised by Eric Schmidt, 9-May-2026.) (Avoid depending on this detail.)
𝐵 ∈ V    &   𝐶 ∈ V    &   𝐷 ∈ V    ⇒   (∪ 𝑥 ∈ 𝐴 {⟨𝑥, 𝐵⟩} = ⟨𝐶, 𝐷⟩ → ∃𝑧 𝐴 = {𝑧})
 
7-May-2026quantgodelALT 47829 There can be no formula asserting its own non-universality; follows the steps of bj-babygodel 37443. (Contributed by Ender Ting, 7-May-2026.) (New usage is discouraged.) (Proof modification is discouraged.)
(𝜑 ↔ ¬ ∀𝑥𝜑)    ⇒   ⊥
 
4-May-2026mplidom 34142 The multivariate polynomials over an integral domain form an integral domain. See ply1idom 26423. (Contributed by Thierry Arnoux, 4-May-2026.)
𝑃 = (𝐼 mPoly 𝑅)    &   (𝜑 → 𝐼 ∈ Fin)    &   (𝜑 → 𝑅 ∈ IDomn)    ⇒   (𝜑 → 𝑃 ∈ IDomn)
 
4-May-2026mplidomlem 34141 Lemma for mplidom 34142. (Contributed by Thierry Arnoux, 4-May-2026.)
𝑃 = (𝐼 mPoly 𝑅)    &   (𝜑 → 𝐼 ∈ Fin)    &   (𝜑 → 𝑅 ∈ IDomn)    &   𝐻 = (𝑓 ∈ 𝐶 ↦ (𝑛 ∈ (ℕ0 ↑m 1o) ↦ (((((𝑗 ∪ {𝑥}) selectVars 𝑅)‘{𝑥})‘𝑓)‘{⟨𝑥, (𝑛‘∅)⟩})))    &   𝐶 = (Base‘𝑆)    &   𝑆 = ((𝑗 ∪ {𝑥}) mPoly 𝑅)    &   𝑈 = (((𝑗 ∪ {𝑥}) ∖ {𝑥}) mPoly 𝑅)    &   𝑄 = (Poly1‘𝑈)    ⇒   (𝜑 → 𝑃 ∈ IDomn)
 
4-May-2026selvply1rhm0 34140 The ring homomorphism 𝐻 built in selvply1rhm 34139 is injective. (Contributed by Thierry Arnoux, 4-May-2026.)
𝐵 = (Base‘𝑃)    &   𝑃 = (𝐼 mPoly 𝑅)    &   𝑈 = ((𝐼 ∖ {𝑋}) mPoly 𝑅)    &   𝑄 = (Poly1‘𝑈)    &   𝐻 = (𝑓 ∈ 𝐵 ↦ (𝑛 ∈ (ℕ0 ↑m 1o) ↦ ((((𝐼 selectVars 𝑅)‘{𝑋})‘𝑓)‘{⟨𝑋, (𝑛‘∅)⟩})))    &   (𝜑 → 𝐼 ∈ 𝑉)    &   (𝜑 → 𝑋 ∈ 𝐼)    &   (𝜑 → 𝑅 ∈ CRing)    &    0 = (0g‘𝑄)    &   𝑍 = (0g‘𝑃)    &   (𝜑 → 𝐹 ∈ 𝐵)    &   (𝜑 → (𝐻‘𝐹) = 0 )    ⇒   (𝜑 → 𝐹 = 𝑍)
 
4-May-2026selvply1rhm 34139 Build a ring homomorphism 𝐻 between the multivariate polynomials 𝑃 with variables in 𝐼 and the univariate polynomials 𝑄 in a single variable 𝑋 element of 𝐼. (Contributed by Thierry Arnoux, 4-May-2026.)
𝐵 = (Base‘𝑃)    &   𝑃 = (𝐼 mPoly 𝑅)    &   𝑈 = ((𝐼 ∖ {𝑋}) mPoly 𝑅)    &   𝑄 = (Poly1‘𝑈)    &   𝐻 = (𝑓 ∈ 𝐵 ↦ (𝑛 ∈ (ℕ0 ↑m 1o) ↦ ((((𝐼 selectVars 𝑅)‘{𝑋})‘𝑓)‘{⟨𝑋, (𝑛‘∅)⟩})))    &   (𝜑 → 𝐼 ∈ 𝑉)    &   (𝜑 → 𝑋 ∈ 𝐼)    &   (𝜑 → 𝑅 ∈ CRing)    ⇒   (𝜑 → 𝐻 ∈ (𝑃 RingHom 𝑄))
 
4-May-2026selvply1rhmlem5 34138 Lemma for selvply1rhm 34139. (Contributed by Thierry Arnoux, 4-May-2026.)
𝐵 = (Base‘𝑃)    &   𝑃 = (𝐼 mPoly 𝑅)    &   𝑈 = ((𝐼 ∖ {𝑋}) mPoly 𝑅)    &   𝑄 = (Poly1‘𝑈)    &   𝐻 = (𝑓 ∈ 𝐵 ↦ (𝑛 ∈ (ℕ0 ↑m 1o) ↦ ((((𝐼 selectVars 𝑅)‘{𝑋})‘𝑓)‘{⟨𝑋, (𝑛‘∅)⟩})))    &   (𝜑 → 𝐼 ∈ 𝑉)    &   (𝜑 → 𝑋 ∈ 𝐼)    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝐹 ∈ 𝐵)    &   𝑀 = (𝑞 ∈ (Base‘({𝑋} mPoly 𝑈)) ↦ (𝑠 ∈ (ℕ0 ↑m 1o) ↦ (𝑞‘{⟨𝑋, (𝑠‘∅)⟩})))    ⇒   (𝜑 → (𝐻‘𝐹) = (𝑀‘(((𝐼 selectVars 𝑅)‘{𝑋})‘𝐹)))
 
4-May-2026selvply1rhmlem4 34137 Lemma for selvply1rhm 34139: The mapping 𝐻 is linear. (Contributed by Thierry Arnoux, 4-May-2026.)
𝐵 = (Base‘𝑃)    &   𝑃 = (𝐼 mPoly 𝑅)    &   𝑈 = ((𝐼 ∖ {𝑋}) mPoly 𝑅)    &   𝑄 = (Poly1‘𝑈)    &   𝐻 = (𝑓 ∈ 𝐵 ↦ (𝑛 ∈ (ℕ0 ↑m 1o) ↦ ((((𝐼 selectVars 𝑅)‘{𝑋})‘𝑓)‘{⟨𝑋, (𝑛‘∅)⟩})))    &   (𝜑 → 𝐼 ∈ 𝑉)    &   (𝜑 → 𝑋 ∈ 𝐼)    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝐹 ∈ 𝐵)    &   (𝜑 → 𝐺 ∈ 𝐵)    ⇒   (𝜑 → (𝐻‘(𝐹(+g‘𝑃)𝐺)) = ((𝐻‘𝐹)(+g‘𝑄)(𝐻‘𝐺)))
 
4-May-2026selvply1rhmlem3 34136 Lemma for selvply1rhm 34139. (Contributed by Thierry Arnoux, 4-May-2026.)
𝐵 = (Base‘𝑃)    &   𝑃 = (𝐼 mPoly 𝑅)    &   𝑈 = ((𝐼 ∖ {𝑋}) mPoly 𝑅)    &   𝑄 = (Poly1‘𝑈)    &   𝐻 = (𝑓 ∈ 𝐵 ↦ (𝑛 ∈ (ℕ0 ↑m 1o) ↦ ((((𝐼 selectVars 𝑅)‘{𝑋})‘𝑓)‘{⟨𝑋, (𝑛‘∅)⟩})))    &   (𝜑 → 𝐼 ∈ 𝑉)    &   (𝜑 → 𝑋 ∈ 𝐼)    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝐹 ∈ 𝐵)    &   (𝜑 → 𝑁 ∈ (ℕ0 ↑m 1o))    ⇒   (𝜑 → ((𝐻‘𝐹)‘𝑁) = ((((𝐼 selectVars 𝑅)‘{𝑋})‘𝐹)‘{⟨𝑋, (𝑁‘∅)⟩}))
 
4-May-2026selvply1rhmlem2 34135 Lemma for selvply1rhm 34139: Image of the ring unit by the mapping 𝐻 (Contributed by Thierry Arnoux, 4-May-2026.)
𝐵 = (Base‘𝑃)    &   𝑃 = (𝐼 mPoly 𝑅)    &   𝑈 = ((𝐼 ∖ {𝑋}) mPoly 𝑅)    &   𝑄 = (Poly1‘𝑈)    &   𝐻 = (𝑓 ∈ 𝐵 ↦ (𝑛 ∈ (ℕ0 ↑m 1o) ↦ ((((𝐼 selectVars 𝑅)‘{𝑋})‘𝑓)‘{⟨𝑋, (𝑛‘∅)⟩})))    &   (𝜑 → 𝐼 ∈ 𝑉)    &   (𝜑 → 𝑋 ∈ 𝐼)    &   (𝜑 → 𝑅 ∈ CRing)    ⇒   (𝜑 → (𝐻‘(1r‘𝑃)) = (1r‘𝑄))
 
4-May-2026selvply1rhmlem1 34134 Lemma for selvply1rhm 34139. (Contributed by Thierry Arnoux, 4-May-2026.)
𝐵 = (Base‘𝑃)    &   𝑃 = (𝐼 mPoly 𝑅)    &   𝑈 = ((𝐼 ∖ {𝑋}) mPoly 𝑅)    &   𝑄 = (Poly1‘𝑈)    &   𝐻 = (𝑓 ∈ 𝐵 ↦ (𝑛 ∈ (ℕ0 ↑m 1o) ↦ ((((𝐼 selectVars 𝑅)‘{𝑋})‘𝑓)‘{⟨𝑋, (𝑛‘∅)⟩})))    &   (𝜑 → 𝐼 ∈ 𝑉)    &   (𝜑 → 𝑋 ∈ 𝐼)    &   (𝜑 → 𝑅 ∈ CRing)    ⇒   (𝜑 → 𝐻:𝐵⟶(Base‘𝑄))
 
4-May-2026selvply1rhmlemb 34133 Lemma for selvply1rhm 34139. (Contributed by Thierry Arnoux, 4-May-2026.)
𝐵 = (Base‘𝑃)    &   𝑃 = ({𝑋} mPoly 𝑅)    &    · = (.r‘𝑃)    &    × = (.r‘𝑄)    &   𝑄 = (Poly1‘𝑅)    &   𝑀 = (𝑓 ∈ 𝐵 ↦ (𝑛 ∈ (ℕ0 ↑m 1o) ↦ (𝑓‘{⟨𝑋, (𝑛‘∅)⟩})))    &   (𝜑 → 𝑋 ∈ 𝑉)    &   (𝜑 → 𝑅 ∈ Ring)    &   (𝜑 → 𝐹 ∈ 𝐵)    &   (𝜑 → 𝐺 ∈ 𝐵)    ⇒   (𝜑 → (𝑀‘(𝐹 · 𝐺)) = ((𝑀‘𝐹) × (𝑀‘𝐺)))
 
4-May-2026selvply1rhmlema 34132 Lemma for selvply1rhm 34139. (Contributed by Thierry Arnoux, 4-May-2026.)
𝐵 = (Base‘𝑃)    &   𝑃 = ({𝑋} mPoly 𝑅)    &    · = (.r‘𝑃)    &    × = (.r‘𝑄)    &   𝑄 = (Poly1‘𝑅)    &   𝑀 = (𝑓 ∈ 𝐵 ↦ (𝑛 ∈ (ℕ0 ↑m 1o) ↦ (𝑓‘{⟨𝑋, (𝑛‘∅)⟩})))    &   (𝜑 → 𝑋 ∈ 𝑉)    &   (𝜑 → 𝑅 ∈ Ring)    &   (𝜑 → 𝐹 ∈ 𝐵)    ⇒   (𝜑 → (𝑀‘𝐹) ∈ (Base‘𝑄))
 
4-May-2026selvascl 34131 The "variable selection" function evaluated at a scalar. (Contributed by Thierry Arnoux, 4-May-2026.)
𝐵 = (Base‘𝑅)    &   𝑃 = (𝐼 mPoly 𝑅)    &   𝐴 = (algSc‘𝑃)    &   𝐶 = (algSc‘𝑇)    &   (𝜑 → 𝐼 ∈ 𝑉)    &   (𝜑 → 𝑋 ∈ 𝐵)    &   𝑈 = ((𝐼 ∖ 𝐽) mPoly 𝑅)    &   𝑇 = (𝐽 mPoly 𝑈)    &   𝐷 = (𝐶 ∘ (algSc‘𝑈))    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝐽 ⊆ 𝐼)    ⇒   (𝜑 → (((𝐼 selectVars 𝑅)‘𝐽)‘(𝐴‘𝑋)) = (𝐷‘𝑋))
 
4-May-2026mplasclco 34130 Case where composing an algebra scalar lifting functions with a scalar leads to a scalar. This is useful when working with selectVars. (Contributed by Thierry Arnoux, 4-May-2026.)
𝑆 = (Base‘𝑅)    &   𝑂 = (𝐽 mPoly 𝑅)    &   𝑃 = (𝐼 mPoly 𝑅)    &   𝑄 = (𝐼 mPoly 𝑂)    &   𝐴 = (algSc‘𝑂)    &   𝐵 = (algSc‘𝑃)    &   𝐶 = (algSc‘𝑄)    &   𝐷 = {ℎ ∈ (ℕ0 ↑m 𝐼) ∣ (◡ℎ “ ℕ) ∈ Fin}    &   𝐸 = {𝑗 ∈ (ℕ0 ↑m 𝐽) ∣ (◡𝑗 “ ℕ) ∈ Fin}    &   (𝜑 → 𝐼 ∈ 𝑉)    &   (𝜑 → 𝐽 ⊆ 𝐼)    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝑋 ∈ 𝑆)    ⇒   (𝜑 → (𝐴 ∘ (𝐵‘𝑋)) = (𝐶‘(𝐴‘𝑋)))
 
4-May-20260mplric 34129 Multivariate polynomials with no variables are isomorphic with the underlying ring. (Contributed by Thierry Arnoux, 4-May-2026.)
𝐵 = (Base‘𝑃)    &   𝑃 = (∅ mPoly 𝑅)    &   (𝜑 → 𝑅 ∈ Ring)    ⇒   (𝜑 → 𝑃 ≃𝑟 𝑅)
 
4-May-20260mplrim 34128 Build a ring isomorphism between multivariate polynomials with no variables and the underlying ring. (Contributed by Thierry Arnoux, 4-May-2026.)
𝐵 = (Base‘𝑃)    &   𝑃 = (∅ mPoly 𝑅)    &   (𝜑 → 𝑅 ∈ Ring)    &   𝐹 = (𝑝 ∈ 𝐵 ↦ (𝑝‘∅))    ⇒   (𝜑 → 𝐹 ∈ (𝑃 RingIso 𝑅))
 
4-May-2026mplnzr 34127 The multivariate polynomials over a nonzero ring form a nonzero ring. (Contributed by Thierry Arnoux, 4-May-2026.)
𝑃 = (𝐼 mPoly 𝑅)    &   (𝜑 → 𝐼 ∈ 𝑉)    &   (𝜑 → 𝑅 ∈ NzRing)    ⇒   (𝜑 → 𝑃 ∈ NzRing)
 
4-May-2026psrnzr 34126 The ring of power series over a nonzero ring form a nonzero ring. (Contributed by Thierry Arnoux, 4-May-2026.)
𝑆 = (𝐼 mPwSer 𝑅)    &   (𝜑 → 𝐼 ∈ 𝑉)    &   (𝜑 → 𝑅 ∈ NzRing)    ⇒   (𝜑 → 𝑆 ∈ NzRing)
 
4-May-2026ricdomn 33833 A ring is a domain if and only if an isomorphic ring is a domain. (Contributed by Thierry Arnoux, 4-May-2026.)
(𝑅 ≃𝑟 𝑆 → (𝑅 ∈ Domn ↔ 𝑆 ∈ Domn))
 
4-May-2026ricdomn1 33832 A ring isomorphism maps a domain to a domain. (Contributed by Thierry Arnoux, 4-May-2026.)
((𝑅 ≃𝑟 𝑆 ∧ 𝑅 ∈ Domn) → 𝑆 ∈ Domn)
 
4-May-2026ricnzr1 33831 A ring isomorphism maps a nonzero ring to a nonzero ring. (Contributed by Thierry Arnoux, 4-May-2026.)
((𝑅 ≃𝑟 𝑆 ∧ 𝑅 ∈ NzRing) → 𝑆 ∈ NzRing)
 
4-May-2026grpidcld 33582 The identity element of a group belongs to the group. (Contributed by Thierry Arnoux, 4-May-2026.)
𝐵 = (Base‘𝐺)    &    0 = (0g‘𝐺)    &   (𝜑 → 𝐺 ∈ Grp)    ⇒   (𝜑 → 0 ∈ 𝐵)
 
4-May-2026ififcom 33128 Commute two nested conditionals. (Contributed by Thierry Arnoux, 4-May-2026.)
if(𝜑, if(𝜓, 𝐴, 𝐵), 𝐵) = if(𝜓, if(𝜑, 𝐴, 𝐵), 𝐵)
 
2-May-2026copsexgw 5460 Version of copsexg 5462 with a disjoint variable condition, which does not require ax-13 2402. (Contributed by GG, 26-Jan-2024.) Shorten proof and remove dependency on ax-10 2178. (Revised by Eric Schmidt, 2-May-2026.)
(𝐴 = ⟨𝑥, 𝑦⟩ → (𝜑 ↔ ∃𝑥∃𝑦(𝐴 = ⟨𝑥, 𝑦⟩ ∧ 𝜑)))
 
1-May-2026vprc 5274 The universal class is not a member of itself (and thus is not a set). Proposition 5.21 of [TakeutiZaring] p. 21; our proof, however, does not depend on the Axiom of Regularity. (Contributed by NM, 23-Aug-1993.) (Proof shortened by BJ, 1-May-2026.)
¬ V ∈ V
 
1-May-2026nvel 5273 The universal class does not belong to any class. (Contributed by FL, 31-Dec-2006.) Prove it without using vprc 5274, which is then proved as an instance of it. (Revised by BJ, 1-May-2026.)
¬ V ∈ 𝐴
 
27-Apr-2026qdiffALT 38217 Alternate proof of qdiff 38216. This is a proof from irrdiff 38215 using excluded middle in a variety of places. (Contributed by Jim Kingdon, 27-Apr-2026.) (Proof modification is discouraged.) (New usage is discouraged.)
(𝐴 ∈ ℝ → (𝐴 ∈ ℚ ↔ ∃𝑞 ∈ ℚ ∃𝑟 ∈ ℚ (𝑞 ≠ 𝑟 ∧ (abs‘(𝐴 − 𝑞)) = (abs‘(𝐴 − 𝑟)))))
 
25-Apr-2026unidif0 5321 The removal of the empty set from a class does not affect its union. (Contributed by NM, 22-Mar-2004.) (Proof shortened by Eric Schmidt, 25-Apr-2026.)
∪ (𝐴 ∖ {∅}) = ∪ 𝐴
 
25-Apr-2026vnex 5271 The universal class does not exist as a set. (Contributed by NM, 4-Jul-2005.) (Proof shortened by BJ, 25-Apr-2026.)
¬ ∃𝑥 𝑥 = V
 
25-Apr-2026vneqv 5270 The universal class is not equal to any setvar. (Contributed by NM, 4-Jul-2005.) Extract from vnex 5271 and shorten proof. (Revised by BJ, 25-Apr-2026.)
¬ 𝑥 = V
 
24-Apr-2026qdiff 38216 The rationals are exactly those reals for which there exist two distinct rationals that are the same distance from the original number. Similar to irrdiff 38215 but here proved with a proof which would also work in constructive mathematics. From an online post by Ingo Blechschmidt. For a proof using irrdiff 38215, see qdiffALT 38217. (Contributed by Jim Kingdon, 24-Apr-2026.)
(𝐴 ∈ ℝ → (𝐴 ∈ ℚ ↔ ∃𝑞 ∈ ℚ ∃𝑟 ∈ ℚ (𝑞 ≠ 𝑟 ∧ (abs‘(𝐴 − 𝑞)) = (abs‘(𝐴 − 𝑟)))))
 
22-Apr-2026sucprcreg 9584 A class is equal to its successor iff it is a proper class (assuming the Axiom of Regularity). (Contributed by NM, 9-Jul-2004.) (Proof shortened by BJ, 16-Apr-2019.) (Proof shortened by SN, 22-Apr-2026.)
(¬ 𝐴 ∈ V ↔ suc 𝐴 = 𝐴)
 
22-Apr-2026nelaneq 9580 A class is not an element of and equal to a class at the same time. Variant of elneq 9579 analogously to elnotel 9595 and en2lp 9591. (Proposed by BJ, 18-Jun-2022.) (Contributed by AV, 18-Jun-2022.) (Proof shortened by TM, 31-Dec-2025.) (Proof shortened by SN, 22-Apr-2026.)
¬ (𝐴 ∈ 𝐵 ∧ 𝐴 = 𝐵)
 
20-Apr-2026cos5t 47869 Five-times-angle formula for cosine, in pure cosine form. (Contributed by Ender Ting, 20-Apr-2026.)
(𝐴 ∈ ℂ → (cos‘(5 · 𝐴)) = (((16 · ((cos‘𝐴)↑5)) − (20 · ((cos‘𝐴)↑3))) + (5 · (cos‘𝐴))))
 
19-Apr-2026trun 5223 The union of transitive classes is transitive. (Contributed by Eric Schmidt, 19-Apr-2026.)
((Tr 𝐴 ∧ Tr 𝐵) → Tr (𝐴 ∪ 𝐵))
 
17-Apr-2026sin5t 47868 Five-times-angle formula for sine, in pure sine form. (Contributed by Ender Ting, 17-Apr-2026.)
(𝐴 ∈ ℂ → (sin‘(5 · 𝐴)) = (((16 · ((sin‘𝐴)↑5)) − (20 · ((sin‘𝐴)↑3))) + (5 · (sin‘𝐴))))
 
17-Apr-2026sin5tlem5 47867 Lemma 5 for quintupled angle sine calculation: sine of triple-angle and double-angle sum, as a polynomial in sine straight. (Contributed by Ender Ting, 17-Apr-2026.)
((𝑁 ∈ ℂ ∧ 𝑀 ∈ ℂ ∧ (𝑁↑2) = (1 − (𝑀↑2))) → ((((3 · 𝑀) − (4 · (𝑀↑3))) · (1 − (2 · (𝑀↑2)))) + (((4 · (𝑁↑3)) − (3 · 𝑁)) · (2 · (𝑀 · 𝑁)))) = (((16 · (𝑀↑5)) − (20 · (𝑀↑3))) + (5 · 𝑀)))
 
17-Apr-2026sin5tlem4 47866 Lemma 4 for quintupled angle sine calculation: expanding lemma 3 result to difference of polynomials. (Contributed by Ender Ting, 17-Apr-2026.)
((𝑁 ∈ ℂ ∧ 𝑀 ∈ ℂ ∧ (𝑁↑2) = (1 − (𝑀↑2))) → (((4 · (𝑁↑3)) − (3 · 𝑁)) · (2 · (𝑀 · 𝑁))) = ((((8 · (𝑀↑5)) − (16 · (𝑀↑3))) + (8 · 𝑀)) − ((6 · 𝑀) − (6 · (𝑀↑3)))))
 
16-Apr-2026goldrarp 47875 The golden ratio is a positive real. (Contributed by Ender Ting, 16-Apr-2026.)
𝐹 = (2 · (cos‘(π / 5)))    ⇒   𝐹 ∈ ℝ+
 
16-Apr-2026goldrapos 47874 Golden ratio is positive. (Contributed by Ender Ting, 16-Apr-2026.)
𝐹 = (2 · (cos‘(π / 5)))    ⇒   0 < 𝐹
 
16-Apr-2026sin5tlem3 47865 Lemma 3 for quintupled angle sine calculation, multiplicating triple angle cosine by double angle sine. (Contributed by Ender Ting, 16-Apr-2026.)
((𝑁 ∈ ℂ ∧ 𝑀 ∈ ℂ ∧ (𝑁↑2) = (1 − (𝑀↑2))) → (((4 · (𝑁↑3)) − (3 · 𝑁)) · (2 · (𝑀 · 𝑁))) = (((4 · ((1 − (2 · (𝑀↑2))) + (𝑀↑4))) − (3 · (1 − (𝑀↑2)))) · (2 · 𝑀)))
 
16-Apr-2026sin5tlem2 47864 Lemma 2 for quintupled angle sine calculation, multiplicating triple angle cosine by cosine straight and converting into sine. (Contributed by Ender Ting, 16-Apr-2026.)
((𝑁 ∈ ℂ ∧ 𝑀 ∈ ℂ ∧ (𝑁↑2) = (1 − (𝑀↑2))) → (((4 · (𝑁↑3)) − (3 · 𝑁)) · 𝑁) = ((4 · ((1 − (2 · (𝑀↑2))) + (𝑀↑4))) − (3 · (1 − (𝑀↑2)))))
 
13-Apr-2026wl-dfclel 38406 The defining characterization of class membership. Unlike the forms on which it is based, it is unrestricted. Proven in Tarski's FOL, from the axiom of (set) extensionality (ax-ext 2733), the definitions df-clel 2836 and df-cleq . (Contributed by BJ, 27-Jun-2019.) Base on wl-dfclel.just 38404. (Revised by Wolf Lammen, 13-Apr-2026.)
(𝐴 ∈ 𝐵 ↔ ∃𝑥(𝑥 = 𝐴 ∧ 𝑥 ∈ 𝐵))
 
13-Apr-2026mh-infprim3bi 37306 An axiom of infinity in primitive symbols not requiring ax-reg 9570. This version of the axiom was designed by Stefan O'Rear for his zf2.nql program, see https://github.com/sorear/metamath-turing-machines 9570. It directly implies ax-inf 9623, but deriving ax-inf2 9626 requires ax-ext 2733 and ax-rep 5232, see mh-inf3sn 37300. (Contributed by Matthew House, 13-Apr-2026.)
(∃𝑦(𝑥 ∈ 𝑦 ∧ ∀𝑧 ∈ 𝑦 {𝑧} ∈ 𝑦) ↔ ¬ ∀𝑦 ¬ ¬ (𝑥 ∈ 𝑦 → ¬ ∀𝑥(𝑥 ∈ 𝑦 → ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))))
 
13-Apr-2026mh-infprim2bi 37305 Shortest possible axiom of infinity in primitive symbols not requiring ax-reg 9570. Deriving ax-inf 9623 or ax-inf2 9626 from this axiom requires ax-ext 2733 and ax-rep 5232, see mh-inf3sn 37300 and inf0 9606. (Contributed by Matthew House, 13-Apr-2026.)
(∃𝑥(∅ ∈ 𝑥 ∧ ∀𝑦 ∈ 𝑥 {𝑦} ∈ 𝑥) ↔ ¬ ∀𝑥 ¬ ∀𝑦∀𝑧(∀𝑤(𝑤 ∈ 𝑦 → ¬ (𝑤 ∈ 𝑥 → ¬ 𝑤 = 𝑧)) → 𝑦 ∈ 𝑥))
 
13-Apr-2026mh-infprim1bi 37304 Shortest possible axiom of infinity in primitive symbols. Deriving ax-inf 9623 or ax-inf2 9626 from this axiom requires ax-ext 2733, ax-rep 5232, and ax-reg 9570, see inf3 9620 and inf0 9606. (Contributed by Matthew House, 13-Apr-2026.)
(∃𝑥(𝑥 ≠ ∅ ∧ 𝑥 ⊆ ∪ 𝑥) ↔ ¬ ∀𝑥 ¬ ∀𝑦 ¬ ∀𝑧((𝑦 ∈ 𝑥 → 𝑦 ∈ 𝑧) → ¬ 𝑧 ∈ 𝑥))
 
13-Apr-2026mh-regprimbi 37303 Shortest possible version of ax-reg 9570 in primitive symbols. The equivalence is nontrivial, but it still follows solely from the axioms of predicate calculus. (Contributed by Matthew House, 13-Apr-2026.)
((∃𝑦 𝑦 ∈ 𝑥 → ∃𝑦(𝑦 ∈ 𝑥 ∧ ∀𝑧(𝑧 ∈ 𝑦 → ¬ 𝑧 ∈ 𝑥))) ↔ ¬ ∀𝑦 ¬ ∀𝑧((𝑦 ∈ 𝑥 → 𝑧 ∈ 𝑦) → ¬ 𝑧 ∈ 𝑥))
 
13-Apr-2026mh-unprimbi 37302 Shortest possible version of ax-un 7740 in primitive symbols. (Contributed by Matthew House, 13-Apr-2026.)
(∃𝑦∀𝑧(∃𝑤(𝑧 ∈ 𝑤 ∧ 𝑤 ∈ 𝑥) → 𝑧 ∈ 𝑦) ↔ ¬ ∀𝑦 ¬ ∀𝑧(𝑧 ∈ 𝑥 → ∀𝑤(𝑤 ∈ 𝑧 → 𝑤 ∈ 𝑦)))
 
13-Apr-2026mh-prprimbi 37301 Shortest possible version of ax-pr 5391 in primitive symbols. (Contributed by Matthew House, 13-Apr-2026.)
(∃𝑧∀𝑤((𝑤 = 𝑥 ∨ 𝑤 = 𝑦) → 𝑤 ∈ 𝑧) ↔ ¬ ∀𝑧(𝑥 ∈ 𝑧 → ¬ 𝑦 ∈ 𝑧))
 
13-Apr-2026mh-inf3sn 37300 Version of inf3 9620 for the set of Zermelo ordinals ∅, {∅}, {{∅}}, {{{∅}}}, etc., where the successor of 𝑦 is {𝑦}. Unlike inf3 9620, the proof does not require ax-reg 9570, since the singleton properties snnz 4737 and sneqr 4800 are sufficient to guarantee that all elements of the sequence are distinct. (Contributed by Matthew House, 13-Apr-2026.)
∃𝑥(∅ ∈ 𝑥 ∧ ∀𝑦 ∈ 𝑥 {𝑦} ∈ 𝑥)    ⇒   ω ∈ V
 
13-Apr-2026mh-inf3f1 37299 A variant of inf3 9620. If 𝐹 is a one-to-one function from 𝐴 into itself, and 𝐵 is an element outside its range, then (rec(𝐹, 𝐵) ↾ ω) is a one-to-one function yielding an infinite sequence of distinct elements from 𝐴. If 𝐴 is a set, we can use this theorem to prove ω ∈ V via f1dmex 7958. (Contributed by Matthew House, 13-Apr-2026.)
(𝜑 → 𝐹:𝐴–1-1→𝐴)    &   (𝜑 → 𝐵 ∈ (𝐴 ∖ ran 𝐹))    ⇒   (𝜑 → (rec(𝐹, 𝐵) ↾ ω):ω–1-1→𝐴)
 
12-Apr-2026nalset 5268 No set contains all sets. Theorem 41 of [Suppes] p. 30. (Contributed by NM, 23-Aug-1993.) Extract exnelv 5267. (Revised by Matthew House, 12-Apr-2026.)
¬ ∃𝑥∀𝑦 𝑦 ∈ 𝑥
 
12-Apr-2026exnelv 5267 For any set 𝑥, there is a set not contained in 𝑥. The proof is based on Russell's paradox. (Contributed by NM, 23-Aug-1993.) Remove use of ax-12 2213 and ax-13 2402. (Revised by BJ, 31-May-2019.) Extract from nalset 5268. (Revised by Matthew House, 12-Apr-2026.)
∃𝑦 ¬ 𝑦 ∈ 𝑥
 
11-Apr-2026indsum 15975 Finite sum of a product with the indicator function / Cartesian product with the indicator function. Note: this theorem cannot be efficiently shortened using sumss2 15872, unless there are some additional auxiliary theorems like (if(𝑥 ∈ 𝐴, 1, 0) · 𝐵) = if(𝑥 ∈ 𝐴, 𝐵, 0). (Contributed by Thierry Arnoux, 14-Aug-2017.) (Proof shortened by AV, 11-Apr-2026.)
(𝜑 → 𝑂 ∈ Fin)    &   (𝜑 → 𝐴 ⊆ 𝑂)    &   ((𝜑 ∧ 𝑥 ∈ 𝑂) → 𝐵 ∈ ℂ)    ⇒   (𝜑 → Σ𝑥 ∈ 𝑂 ((((𝟭‘𝑂)‘𝐴)‘𝑥) · 𝐵) = Σ𝑥 ∈ 𝐴 𝐵)
 
11-Apr-2026indval0 12305 The indicator function generator does not generate a (meaningful) indicator function for a class which is not a subset of the domain. (Contributed by AV, 11-Apr-2026.)
(¬ 𝐴 ⊆ 𝑂 → ((𝟭‘𝑂)‘𝐴) = ∅)
 
10-Apr-2026ppivalnn 48661 Value of the prime-counting function pi for positive integers, according to Ján Mináč, see statement in [Ribenboim], p. 181. (Contributed by AV, 10-Apr-2026.)
(𝑁 ∈ ℕ → (π‘𝑁) = Σ𝑘 ∈ (2...𝑁)(⌊‘((((!‘(𝑘 − 1)) + 1) / 𝑘) − (⌊‘((!‘(𝑘 − 1)) / 𝑘)))))
 
10-Apr-2026ppivalnnprm 48654 Value of a term of the prime-counting function pi for positive integers, according to Ján Mináč, for a prime number. (Contributed by AV, 10-Apr-2026.)
(𝑃 ∈ ℙ → (⌊‘((((!‘(𝑃 − 1)) + 1) / 𝑃) − (⌊‘((!‘(𝑃 − 1)) / 𝑃)))) = 1)
 
10-Apr-2026flmrecm1 48357 The floor of an integer minus the reciprocal of a positive integer is the integer minus 1. (Contributed by AV, 10-Apr-2026.)
((𝑀 ∈ ℤ ∧ 𝑁 ∈ ℕ) → (⌊‘(𝑀 − (1 / 𝑁))) = (𝑀 − 1))
 
10-Apr-2026nnge2recfl0 48356 The floor of the reciprocal of an integer greater than 1 is 0. (Contributed by AV, 10-Apr-2026.)
(𝑁 ∈ (ℤ≥‘2) → (⌊‘(1 / 𝑁)) = 0)
 
10-Apr-2026prmssuz2 16852 The primes are integers greater than 1. (Contributed by AV, 10-Apr-2026.)
ℙ ⊆ (ℤ≥‘2)
 
10-Apr-2026indsumhash 15976 The finite sum of the indicator function is the number of elements of the corresponding subset. (Contributed by AV, 10-Apr-2026.)
1 = ((𝟭‘𝑂)‘𝐴)    ⇒   ((𝑂 ∈ Fin ∧ 𝐴 ⊆ 𝑂) → Σ𝑘 ∈ 𝑂 ( 1 ‘𝑘) = (♯‘𝐴))
 
10-Apr-2026fsumconst1 15937 The sum of 1 over a finite set equals the size of the set. (Contributed by AV, 10-Apr-2026.)
(𝐴 ∈ Fin → Σ𝑘 ∈ 𝐴 1 = (♯‘𝐴))
 
10-Apr-2026nnge2recico01 13619 The reciprocal of an integer greater than 1 is in the right open interval between 0 and 1. (Contributed by AV, 10-Apr-2026.)
(𝑁 ∈ (ℤ≥‘2) → (1 / 𝑁) ∈ (0[,)1))
 
10-Apr-2026fvindre 12309 The range of the indicator function is a subset of ℝ. (Contributed by AV, 10-Apr-2026.)
(((𝑂 ∈ Fin ∧ 𝐴 ⊆ 𝑂) ∧ 𝑋 ∈ 𝑂) → (((𝟭‘𝑂)‘𝐴)‘𝑋) ∈ ℝ)
 
9-Apr-2026rediv11d 43482 One-to-one relationship for division. (Contributed by SN, 9-Apr-2026.)
(𝜑 → 𝐴 ∈ ℝ)    &   (𝜑 → 𝐵 ∈ ℝ)    &   (𝜑 → 𝐶 ∈ ℝ)    &   (𝜑 → 𝐶 ≠ 0)    ⇒   (𝜑 → ((𝐴 /ℝ 𝐶) = (𝐵 /ℝ 𝐶) ↔ 𝐴 = 𝐵))
 
9-Apr-2026redivdird 43481 Distribution of division over addition. (Contributed by SN, 9-Apr-2026.)
(𝜑 → 𝐴 ∈ ℝ)    &   (𝜑 → 𝐵 ∈ ℝ)    &   (𝜑 → 𝐶 ∈ ℝ)    &   (𝜑 → 𝐶 ≠ 0)    ⇒   (𝜑 → ((𝐴 + 𝐵) /ℝ 𝐶) = ((𝐴 /ℝ 𝐶) + (𝐵 /ℝ 𝐶)))
 
9-Apr-2026rediv23d 43480 A "commutative"/associative law for division. (Contributed by SN, 9-Apr-2026.)
(𝜑 → 𝐴 ∈ ℝ)    &   (𝜑 → 𝐵 ∈ ℝ)    &   (𝜑 → 𝐶 ∈ ℝ)    &   (𝜑 → 𝐶 ≠ 0)    ⇒   (𝜑 → ((𝐴 · 𝐵) /ℝ 𝐶) = ((𝐴 /ℝ 𝐶) · 𝐵))
 
9-Apr-2026redivrec2d 43479 Relationship between division and reciprocal. (Contributed by SN, 9-Apr-2026.)
(𝜑 → 𝐴 ∈ ℝ)    &   (𝜑 → 𝐵 ∈ ℝ)    &   (𝜑 → 𝐵 ≠ 0)    ⇒   (𝜑 → (𝐴 /ℝ 𝐵) = ((1 /ℝ 𝐵) · 𝐴))
 
8-Apr-2026ppivalnnnprm 48657 Value of a term of the prime-counting function pi for positive integers, according to Ján Miná&ccaron, for a non-prime number greater than 1. (Contributed by AV, 8-Apr-2026.)
((𝑁 ∈ (ℤ≥‘2) ∧ 𝑁 ∉ ℙ) → (⌊‘((((!‘(𝑁 − 1)) + 1) / 𝑁) − (⌊‘((!‘(𝑁 − 1)) / 𝑁)))) = 0)
 
8-Apr-2026ppivalnn4 48656 Value of the term of the prime-counting function pi for positive integers, according to Ján Mináč, for 4. (Contributed by AV, 8-Apr-2026.)
(⌊‘((((!‘(4 − 1)) + 1) / 4) − (⌊‘((!‘(4 − 1)) / 4)))) = 0
 
7-Apr-2026nprmdvdsfacm1 48653 A non-prime integer greater than 5 divides the factorial of the integer decreased by 1 (see remark in [Ribenboim] p. 181). Note: not valid for 𝑁 = 4, but for 𝑁 = 1! (Contributed by AV, 7-Apr-2026.)
((𝑁 ∈ (ℤ≥‘6) ∧ 𝑁 ∉ ℙ) → 𝑁 ∥ (!‘(𝑁 − 1)))
 
7-Apr-2026nprmdvdsfacm1lem4 48652 Lemma 4 for nprmdvdsfacm1 48653. (Contributed by AV, 7-Apr-2026.)
((𝑁 ∈ (ℤ≥‘6) ∧ 𝐴 ∈ (2..^𝑁) ∧ 𝑁 = (𝐴↑2)) → 𝑁 ∥ (!‘(𝑁 − 1)))
 
7-Apr-2026nprmdvdsfacm1lem3 48651 Lemma 3 for nprmdvdsfacm1 48653. (Contributed by AV, 7-Apr-2026.)
((𝑁 ∈ (ℤ≥‘6) ∧ 𝐴 ∈ (2..^𝑁) ∧ 𝑁 = (𝐴↑2)) → (2 · 𝐴) < (𝑁 − 1))
 
7-Apr-2026nprmdvdsfacm1lem2 48650 Lemma 2 for nprmdvdsfacm1 48653. (Contributed by AV, 7-Apr-2026.)
((𝑁 ∈ (ℤ≥‘6) ∧ 𝐴 ∈ (2..^𝑁) ∧ 𝑁 = (𝐴↑2)) → 3 ≤ 𝐴)
 
7-Apr-2026nprmdvdsfacm1lem1 48649 Lemma 1 for nprmdvdsfacm1 48653. (Contributed by AV, 7-Apr-2026.)
((𝑁 ∈ (ℤ≥‘6) ∧ 𝐴 ∈ (2..^𝑁) ∧ 𝑁 = (𝐴↑2)) → 𝑁 ∥ (𝐴 · (2 · 𝐴)))
 
7-Apr-20262timesltsqm1 48393 Two times an integer greater than 2 is less than the square of the integer minus 1. (Contributed by AV, 7-Apr-2026.)
(𝐴 ∈ (ℤ≥‘3) → (2 · 𝐴) < ((𝐴↑2) − 1))
 
7-Apr-2026wl-dfcleq 38405 The defining characterization of class equality. This version of df-cleq 2753 has no restrictions, unlike the forms on which it is based. It is proved in Tarski's FOL from the axiom of extensionality (ax-ext 2733), the definition of class equality (df-cleq 2753), and the definition of class membership (df-clel 2836).

Its forward implication is known as "class extensionality". (Contributed by NM, 15-Sep-1993.) (Revised by BJ, 24-Jun-2019.) Base on wl-dfcleq.just 38401. (Revised by Wolf Lammen, 7-Apr-2026.)

(𝐴 = 𝐵 ↔ ∀𝑥(𝑥 ∈ 𝐴 ↔ 𝑥 ∈ 𝐵))
 
7-Apr-2026wl-dfclel.just 38404 Add a hypothesis to wl-dfclel.basic 38403, that permits alpha-renaming. (Contributed by Wolf Lammen, 7-Apr-2026.)
(∃𝑥(𝑥 = 𝐴 ∧ 𝑥 ∈ 𝐵) ↔ ∃𝑦(𝑦 = 𝐴 ∧ 𝑦 ∈ 𝐵))    ⇒   (𝐴 ∈ 𝐵 ↔ ∃𝑥(𝑥 = 𝐴 ∧ 𝑥 ∈ 𝐵))
 
7-Apr-2026wl-dfcleq.just 38401 The hypotheses added to this version of df-cleq 2753 address the following:

1. Equality of classes is an equivalence relation, as expected of equality.

2. Equality of classes obeys the Law of Indiscernibles (Leibniz's Law), and is compatible with class membership.

3. Alpha-renaming is explicitly permitted.

(Contributed by Wolf Lammen, 7-Apr-2026.)

(∀𝑥(𝑥 ∈ 𝐴 ↔ 𝑥 ∈ 𝐵) ↔ ∀𝑦(𝑦 ∈ 𝐴 ↔ 𝑦 ∈ 𝐵))    &   𝐴 = 𝐴    &   (𝐴 = 𝐵 → (𝐵 = 𝐶 → 𝐶 = 𝐴))    &   (𝐴 = 𝐵 → (𝐴 ∈ 𝐶 → 𝐵 ∈ 𝐶))    &   (𝐴 = 𝐵 → (𝐶 ∈ 𝐴 → 𝐶 ∈ 𝐵))    ⇒   (𝐴 = 𝐵 ↔ ∀𝑥(𝑥 ∈ 𝐴 ↔ 𝑥 ∈ 𝐵))
 
7-Apr-2026elALTtco 37239 Derivation of el 5406 from ax-tco 37230. Use el 5406 instead. (Contributed by Matthew House, 7-Apr-2026.) (Proof modification is discouraged.) (New usage is discouraged.)
∃𝑦 𝑥 ∈ 𝑦
 
7-Apr-2026axnulregtco 37238 Derivation of ax-nul 5260 from ax-reg 9570 and ax-tco 37230. Use ax-nul 5260 instead. (Contributed by Matthew House, 7-Apr-2026.) (Proof modification is discouraged.) (New usage is discouraged.)
∃𝑥∀𝑦 ¬ 𝑦 ∈ 𝑥
 
7-Apr-2026axtco1 37231 Strong form of the Axiom of Transitive Containment. See ax-tco 37230 for more information. In particular, this theorem generalizes the statement of ax-tco 37230, allowing it to be written with only three variables, since 𝑥 need not be distinct from both 𝑧 and 𝑤. (Contributed by Matthew House, 7-Apr-2026.)
∃𝑦(𝑥 ∈ 𝑦 ∧ ∀𝑧(𝑧 ∈ 𝑦 → ∀𝑤(𝑤 ∈ 𝑧 → 𝑤 ∈ 𝑦)))
 
6-Apr-2026nprmmul2 48554 Special factorization of a non-prime integer greater than 3. (Contributed by AV, 6-Apr-2026.)
(𝑁 ∈ (ℤ≥‘4) → (𝑁 ∉ ℙ ↔ ∃𝑎 ∈ (2..^𝑁)∃𝑏 ∈ (2..^𝑁)(𝑎 ≤ 𝑏 ∧ 𝑁 = (𝑎 · 𝑏))))
 
6-Apr-2026muldvdsfacm1 48401 The product of two different positive integers less than a third integer divides the factorial of the third integer decreased by 1. By assumption, the third integer must be greater than 3. (Contributed by AV, 6-Apr-2026.)
((𝐴 ∈ (1..^𝐵) ∧ 𝐵 ∈ (1..^𝑁)) → (𝐴 · 𝐵) ∥ (!‘(𝑁 − 1)))
 
6-Apr-2026muldvdsfacgt 48400 The product of two different positive integers divides the factorial of the bigger integer. (Contributed by AV, 6-Apr-2026.)
(𝐴 ∈ (1..^𝐵) → (𝐴 · 𝐵) ∥ (!‘𝐵))
 
6-Apr-2026facnn0dvdsfac 48399 The factorial of a nonnegative integer divides the factorial of an integer which is greater than or equal to the first integer. (Contributed by AV, 6-Apr-2026.)
(𝑀 ∈ (0...𝑁) → (!‘𝑀) ∥ (!‘𝑁))
 
6-Apr-20262timesltsq 48392 Two times an integer greater than 2 is less than the square of the integer. (Contributed by AV, 6-Apr-2026.)
(𝐴 ∈ (ℤ≥‘3) → (2 · 𝐴) < (𝐴↑2))
 
6-Apr-2026ttc0el 37293 A transitive closure contains ∅ as an element iff it is nonempty, assuming Regularity and Transitive Containment. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ≠ ∅ ↔ ∅ ∈ TC+ 𝐴)
 
6-Apr-2026dfttc3g 37292 The transitive closure of a set 𝐴 is (TC‘𝐴), assuming Transitive Containment. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ∈ 𝑉 → TC+ 𝐴 = (TC‘𝐴))
 
6-Apr-2026ttcexbi 37291 A class is a set iff its transitive closure is a set, assuming Transitive Containment. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ∈ V ↔ TC+ 𝐴 ∈ V)
 
6-Apr-2026ttcexg 37290 The transitive closure of a set is a set, assuming Transitive Containment. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ∈ 𝑉 → TC+ 𝐴 ∈ V)
 
6-Apr-2026elttcirr 37289 Irreflexivity of 𝐴 ∈ TC+ 𝐵 relationship. This is a consequence of Regularity, but it does not require Transitive Containment. We use the alternative expression dfttc4 37288 to construct a set in which 𝐴 is both ∈-minimal and not ∈-minimal. (Contributed by Matthew House, 6-Apr-2026.)
¬ 𝐴 ∈ TC+ 𝐴
 
6-Apr-2026dfttc4 37288 An alternative expression for the transitive closure of a class, assuming Regularity. A set 𝑥 is contained in the transitive closure of 𝐴 iff we can construct an ∈-chain from 𝑥 to an element of 𝐴. This weak definition is primarily useful for proving elttcirr 37289. (Contributed by Matthew House, 6-Apr-2026.)
TC+ 𝐴 = {𝑥 ∣ ∃𝑦((𝐴 ∩ 𝑦) ≠ ∅ ∧ ∀𝑧 ∈ 𝑦 ((𝑧 ∩ 𝑦) = ∅ → 𝑧 = 𝑥))}
 
6-Apr-2026dfttc4lem2 37287 Lemma for dfttc4 37288. (Contributed by Matthew House, 6-Apr-2026.)
𝐵 = {𝑥 ∣ ∃𝑦((𝐴 ∩ 𝑦) ≠ ∅ ∧ ∀𝑧 ∈ 𝑦 ((𝑧 ∩ 𝑦) = ∅ → 𝑧 = 𝑥))}    ⇒   (𝐴 ⊆ 𝐵 ∧ Tr 𝐵)
 
6-Apr-2026dfttc4lem1 37286 Lemma for dfttc4 37288. (Contributed by Matthew House, 6-Apr-2026.)
𝐵 = {𝑥 ∣ ∃𝑦((𝐴 ∩ 𝑦) ≠ ∅ ∧ ∀𝑧 ∈ 𝑦 ((𝑧 ∩ 𝑦) = ∅ → 𝑧 = 𝑥))}    &   𝐶 ∈ V    &   𝐷 ∈ V    ⇒   (((𝐴 ∩ 𝐶) ≠ ∅ ∧ ∀𝑧 ∈ 𝐶 ((𝑧 ∩ 𝐶) = ∅ → 𝑧 = 𝐷)) → 𝐷 ∈ 𝐵)
 
6-Apr-2026ttc0elw 37285 If a transitive closure is a set, then it contains ∅ as an element iff it is nonempty, assuming Regularity. If we also assume Transitive Containment, then we can remove the TC+ 𝐴 ∈ 𝑉 hypothesis, see ttc0el 37293. (Contributed by Matthew House, 6-Apr-2026.)
(TC+ 𝐴 ∈ 𝑉 → (𝐴 ≠ ∅ ↔ ∅ ∈ TC+ 𝐴))
 
6-Apr-2026ttcwf3 37284 The sets whose transitive closures are sets are precisely the well-founded sets, assuming Regularity. (Contributed by Matthew House, 6-Apr-2026.)
(TC+ 𝐴 ∈ V ↔ 𝐴 ∈ ∪ (𝑅1 “ On))
 
6-Apr-2026ttcwf2 37283 If a transitive closure class is a set, then it is well-founded, assuming Regularity. (Contributed by Matthew House, 6-Apr-2026.)
(TC+ 𝐴 ∈ V ↔ TC+ 𝐴 ∈ ∪ (𝑅1 “ On))
 
6-Apr-2026ttcwf 37282 A set is well-founded iff its transitive closure is well-founded. As a corollary, the transitive closure of any well-founded set is a set. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ∈ ∪ (𝑅1 “ On) ↔ TC+ 𝐴 ∈ ∪ (𝑅1 “ On))
 
6-Apr-2026dfttc3gw 37281 If the transitive closure of 𝐴 is a set, then its value is (TC‘𝐴). If we assume Transitive Containment, then we can weaken the hypothesis to 𝐴 ∈ 𝑉, see dfttc3g 37292. (Contributed by Matthew House, 6-Apr-2026.)
(TC+ 𝐴 ∈ 𝑉 → TC+ 𝐴 = (TC‘𝐴))
 
6-Apr-2026ttcsntrsucg 37280 The singleton transitive closure of a transitive set is its successor. (Contributed by Matthew House, 6-Apr-2026.)
((𝐴 ∈ 𝑉 ∧ Tr 𝐴) → TC+ {𝐴} = suc 𝐴)
 
6-Apr-2026ttcsnexbig 37279 The transitive closure of a set is a set iff its singleton transitive closure is a set. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ∈ 𝑉 → (TC+ 𝐴 ∈ V ↔ TC+ {𝐴} ∈ V))
 
6-Apr-2026ttcsnexg 37278 If the transitive closure of a class is a set, then its singleton transitive closure is a set. (Contributed by Matthew House, 6-Apr-2026.)
(TC+ 𝐴 ∈ 𝑉 → TC+ {𝐴} ∈ V)
 
6-Apr-2026ttcsng 37277 Relationship between TC+ {𝐴} and TC+ 𝐴: the former contains the additional element 𝐴. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ∈ 𝑉 → TC+ {𝐴} = (TC+ 𝐴 ∪ {𝐴}))
 
6-Apr-2026ttcsnmin 37276 The singleton transitive closure is the minimal transitive class containing 𝐴 as an element. (Contributed by Matthew House, 6-Apr-2026.)
((𝐴 ∈ 𝐵 ∧ Tr 𝐵) → TC+ {𝐴} ⊆ 𝐵)
 
6-Apr-2026ttcsnidg 37275 The singleton transitive closure contains its argument 𝐴 as an element. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ∈ 𝑉 → 𝐴 ∈ TC+ {𝐴})
 
6-Apr-2026ttcsnssg 37274 The transitive closure is contained in the singleton transitive closure. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ∈ 𝑉 → TC+ 𝐴 ⊆ TC+ {𝐴})
 
6-Apr-2026ttcpwss 37273 The transitive closure of a power class is contained in the power class of the transitive closure. (Contributed by Matthew House, 6-Apr-2026.)
TC+ 𝒫 𝐴 ⊆ 𝒫 TC+ 𝐴
 
6-Apr-2026ttciun 37272 Distribute indexed union through a transitive closure. (Contributed by Matthew House, 6-Apr-2026.)
TC+ ∪ 𝑥 ∈ 𝐴 𝐵 = ∪ 𝑥 ∈ 𝐴 TC+ 𝐵
 
6-Apr-2026ttcuni 37271 Distribute union of a class through a transitive closure. (Contributed by Matthew House, 6-Apr-2026.)
TC+ ∪ 𝐴 = ∪ TC+ 𝐴
 
6-Apr-2026ttcun 37270 Distribute union of two classes through a transitive closure. (Contributed by Matthew House, 6-Apr-2026.)
TC+ (𝐴 ∪ 𝐵) = (TC+ 𝐴 ∪ TC+ 𝐵)
 
6-Apr-2026ttciunun 37269 Relationship between TC+ 𝐴 and ∪ 𝑥 ∈ 𝐴TC+ 𝑥: we can decompose TC+ 𝐴 into the elements of ∪ 𝑥 ∈ 𝐴TC+ 𝑥 plus the elements of 𝐴 itself. (Contributed by Matthew House, 6-Apr-2026.)
TC+ 𝐴 = (∪ 𝑥 ∈ 𝐴 TC+ 𝑥 ∪ 𝐴)
 
6-Apr-2026ttcuniun 37268 Relationship between TC+ 𝐴 and TC+ ∪ 𝐴: we can decompose TC+ 𝐴 into the elements of TC+ ∪ 𝐴 plus the elements of 𝐴 itself. (Contributed by Matthew House, 6-Apr-2026.)
TC+ 𝐴 = (TC+ ∪ 𝐴 ∪ 𝐴)
 
6-Apr-2026csbttc 37267 Distribute proper substitution through a transitive closure. (Contributed by Matthew House, 6-Apr-2026.)
⦋𝐴 / 𝑥⦌TC+ 𝐵 = TC+ ⦋𝐴 / 𝑥⦌𝐵
 
6-Apr-2026ttc00 37266 A class has an empty transitive closure iff it is the empty set. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 = ∅ ↔ TC+ 𝐴 = ∅)
 
6-Apr-2026ttc0 37265 The transitive closure of the empty set is the empty set. (Contributed by Matthew House, 6-Apr-2026.)
TC+ ∅ = ∅
 
6-Apr-2026dfttc2g 37264 A shorter expression for the transitive closure of a set. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ∈ 𝑉 → TC+ 𝐴 = ∪ (rec((𝑥 ∈ V ↦ ∪ 𝑥), 𝐴) “ ω))
 
6-Apr-2026elttctr 37263 Transitivity of 𝐴 ∈ TC+ 𝐵 relationship. (Contributed by Matthew House, 6-Apr-2026.)
((𝐴 ∈ TC+ 𝐵 ∧ 𝐵 ∈ TC+ 𝐶) → 𝐴 ∈ TC+ 𝐶)
 
6-Apr-2026ssttctr 37262 Transitivity of 𝐴 ⊆ TC+ 𝐵 relationship. (Contributed by Matthew House, 6-Apr-2026.)
((𝐴 ⊆ TC+ 𝐵 ∧ 𝐵 ⊆ TC+ 𝐶) → 𝐴 ⊆ TC+ 𝐶)
 
6-Apr-2026ttcidm 37261 The transitive closure operation is idempotent. (Contributed by Matthew House, 6-Apr-2026.)
TC+ TC+ 𝐴 = TC+ 𝐴
 
6-Apr-2026ttctrid 37260 The transitive closure of a transitive class is the class itself. (Contributed by Matthew House, 6-Apr-2026.)
(Tr 𝐴 → TC+ 𝐴 = 𝐴)
 
6-Apr-2026ttcel2 37259 Elements turn into subclasses upon taking transitive closures. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ∈ 𝐵 → TC+ 𝐴 ⊆ TC+ 𝐵)
 
6-Apr-2026ttcel 37258 A transitive closure contains the transitive closures of all its elements. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ∈ TC+ 𝐵 → TC+ 𝐴 ⊆ TC+ 𝐵)
 
6-Apr-2026ttcss2 37257 The subclass relationship is inherited by transitive closures. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ⊆ 𝐵 → TC+ 𝐴 ⊆ TC+ 𝐵)
 
6-Apr-2026ttcss 37256 A transitive closure contains the transitive closures of all its subclasses. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ⊆ TC+ 𝐵 → TC+ 𝐴 ⊆ TC+ 𝐵)
 
6-Apr-2026ttcexrg 37255 If the transitive closure of a class is a set, then the class is a set. (Contributed by Matthew House, 6-Apr-2026.)
(TC+ 𝐴 ∈ 𝑉 → 𝐴 ∈ V)
 
6-Apr-2026ttcmin 37254 The transitive closure of 𝐴 is a subclass of every transitive class containing 𝐴. (Contributed by Matthew House, 6-Apr-2026.)
((𝐴 ⊆ 𝐵 ∧ Tr 𝐵) → TC+ 𝐴 ⊆ 𝐵)
 
6-Apr-2026ttctr3 37253 The transitive closure of a class is transitive. (Contributed by Matthew House, 6-Apr-2026.)
∪ TC+ 𝐴 ⊆ TC+ 𝐴
 
6-Apr-2026ttctr2 37252 The transitive closure of a class is transitive. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ∈ TC+ 𝐵 → 𝐴 ⊆ TC+ 𝐵)
 
6-Apr-2026ttctr 37251 The transitive closure of a class is transitive. (Contributed by Matthew House, 6-Apr-2026.)
Tr TC+ 𝐴
 
6-Apr-2026ttcid 37250 The transitive closure contains its argument as a subclass. (Contributed by Matthew House, 6-Apr-2026.)
𝐴 ⊆ TC+ 𝐴
 
6-Apr-2026nfttc 37249 Bound-variable hypothesis builder for transitive closure. (Contributed by Matthew House, 6-Apr-2026.)
Ⅎ𝑥𝐴    ⇒   Ⅎ𝑥TC+ 𝐴
 
6-Apr-2026ttceqd 37248 Equality deduction for transitive closure. (Contributed by Matthew House, 6-Apr-2026.)
(𝜑 → 𝐴 = 𝐵)    ⇒   (𝜑 → TC+ 𝐴 = TC+ 𝐵)
 
6-Apr-2026ttceqi 37247 Equality inference for transitive closure. (Contributed by Matthew House, 6-Apr-2026.)
𝐴 = 𝐵    ⇒   TC+ 𝐴 = TC+ 𝐵
 
6-Apr-2026ttceq 37246 Equality theorem for transitive closure. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 = 𝐵 → TC+ 𝐴 = TC+ 𝐵)
 
6-Apr-2026df-ttc 37245 Transitive closure of a class. Unlike (TC‘𝐴) (see df-tc 9720), this definition works even if 𝐴 or its transitive closure is a proper class. Note that unless we assume Transitive Containment, the transitive closure of a set may be a proper class. If we only assume Regularity, then the class of sets whose transitive closure is a set is precisely the class of well-founded sets, see ttcwf3 37284. (Contributed by Matthew House, 6-Apr-2026.)
TC+ 𝐴 = ∪ 𝑥 ∈ 𝐴 ∪ (rec((𝑦 ∈ V ↦ ∪ 𝑦), {𝑥}) “ ω)
 
6-Apr-2026cttc 37244 Extend class notation with the transitive closure of a class. (Contributed by Matthew House, 6-Apr-2026.)
class TC+ 𝐴
 
6-Apr-2026tr0el 37243 Every nonempty transitive class contains the empty set ∅ as an element, a consequence of Regularity and Transitive Containment. (Contributed by Matthew House, 6-Apr-2026.)
((𝐴 ≠ ∅ ∧ Tr 𝐴) → ∅ ∈ 𝐴)
 
6-Apr-2026tr0elw 37242 Every nonempty transitive set contains the empty set ∅ as an element, a consequence of Regularity. If we assume Transitive Containment, then we can omit the 𝐴 ∈ 𝑉 hypothesis, see tr0el 37243. (Contributed by Matthew House, 6-Apr-2026.)
((𝐴 ∈ 𝑉 ∧ 𝐴 ≠ ∅ ∧ Tr 𝐴) → ∅ ∈ 𝐴)
 
6-Apr-2026tz9.1tco 37241 Version of tz9.1 9714 derived from ax-tco 37230. (Contributed by Matthew House, 6-Apr-2026.)
𝐴 ∈ V    ⇒   ∃𝑥(𝐴 ⊆ 𝑥 ∧ Tr 𝑥 ∧ ∀𝑦((𝐴 ⊆ 𝑦 ∧ Tr 𝑦) → 𝑥 ⊆ 𝑦))
 
6-Apr-2026tz9.1ctco 37240 Version of tz9.1c 9715 derived from ax-tco 37230. (Contributed by Matthew House, 6-Apr-2026.)
𝐴 ∈ V    ⇒   ∩ {𝑥 ∣ (𝐴 ⊆ 𝑥 ∧ Tr 𝑥)} ∈ V
 
6-Apr-2026axuntco 37237 Derivation of ax-un 7740 from ax-tco 37230. Use ax-un 7740 instead. (Contributed by Matthew House, 6-Apr-2026.) (Proof modification is discouraged.) (New usage is discouraged.)
∃𝑦∀𝑧(∃𝑤(𝑧 ∈ 𝑤 ∧ 𝑤 ∈ 𝑥) → 𝑧 ∈ 𝑦)
 
6-Apr-2026axtcond 37236 A version of the Axiom of Transitive Containment with no distinct variable conditions. Usage of this theorem is discouraged because it depends on ax-13 2402. (Contributed by Matthew House, 6-Apr-2026.) (New usage is discouraged.)
∃𝑦∀𝑧((𝑧 = 𝑥 ∨ 𝑧 ∈ 𝑦) → ∀𝑥(𝑥 ∈ 𝑧 → 𝑥 ∈ 𝑦))
 
6-Apr-2026axtco2g 37235 Weak form of the Axiom of Transitive Containment using class variables and abbreviations. See ax-tco 37230 for more information. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ∈ 𝑉 → ∃𝑥(𝐴 ⊆ 𝑥 ∧ Tr 𝑥))
 
6-Apr-2026axtco1g 37234 Strong form of the Axiom of Transitive Containment using class variables and abbreviations. See ax-tco 37230 for more information. (Contributed by Matthew House, 6-Apr-2026.)
(𝐴 ∈ 𝑉 → ∃𝑥(𝐴 ∈ 𝑥 ∧ Tr 𝑥))
 
6-Apr-2026axtco1from2 37233 Strong form axtco1 37231 of the Axiom of Transitive Containment, derived from the weak form axtco2 37232. See ax-tco 37230 for more information. As written, the proof uses ax-pr 5391 via el 5406, but we could alternatively use ax-pow 5327 via elALT2 5331. Use axtco1 37231 instead. (Contributed by Matthew House, 6-Apr-2026.) (Proof modification is discouraged.) (New usage is discouraged.)
∃𝑦(𝑥 ∈ 𝑦 ∧ ∀𝑧(𝑧 ∈ 𝑦 → ∀𝑤(𝑤 ∈ 𝑧 → 𝑤 ∈ 𝑦)))
 
6-Apr-2026axtco2 37232 Weak form of the Axiom of Transitive Containment. See ax-tco 37230 for more information. In particular, this theorem shows the derivation of the weak form from the strong form. (Contributed by Matthew House, 6-Apr-2026.)
∃𝑦∀𝑧((𝑧 = 𝑥 ∨ 𝑧 ∈ 𝑦) → ∀𝑤(𝑤 ∈ 𝑧 → 𝑤 ∈ 𝑦))
 
6-Apr-2026ax-tco 37230 The Axiom of Transitive Containment of ZF set theory. It was derived as axtco 37229 above and is therefore redundant if we assume ax-ext 2733, ax-rep 5232 and ax-inf2 9626, but we state it as a separate axiom here so that its uses can be identified more easily. It states that a transitive set 𝑦 exists that contains a given set 𝑥. In particular, the transitive closure of 𝑥 is a set, since it is a subset of 𝑦, see df-tc 9720.

Traditionally, this statement is not counted as an axiom at all, but as a theorem from Replacement and Infinity. In fact, from the transitive closure of 𝑥 we can construct the set of iterated unions of 𝑥 (and vice versa), and Skolem took the existence of the latter set as a motivation for introducing the Axiom of Replacement. But Transitive Containment is strictly weaker than either of those axioms, so many authors identify it as its own axiom when investigating subsystems of ZF, such as Zermelo set theory or finitist set theory. We follow this separation in order to avoid nonessential usage of the stronger axioms.

There are two main versions of this axiom that appear in the literature: the strong form ∃𝑦(𝑥 ∈ 𝑦 ∧ Tr 𝑦), see axtco1 37231 and axtco1g 37234, and the weak form ∃𝑦(𝑥 ⊆ 𝑦 ∧ Tr 𝑦), see axtco2 37232 and axtco2g 37235. The weak form follows directly from the strong form, see axtco2 37232. But the strong form only follows from the weak form if we allow el 5406 or one of its variants, see axtco1from2 37233. We take the strong form here as the axiom, since it is slightly shorter when expanded to primitive symbols. Yet the weak form turns out to be more suitable for axtcond 37236 for reasons of syntax. (Contributed by Matthew House, 6-Apr-2026.)

∃𝑦(𝑥 ∈ 𝑦 ∧ ∀𝑧(𝑧 ∈ 𝑦 → ∀𝑤(𝑤 ∈ 𝑧 → 𝑤 ∈ 𝑦)))
 
6-Apr-2026axtco 37229 Axiom of Transitive Containment, derived as a theorem from ax-ext 2733, ax-rep 5232, and ax-inf2 9626. Use ax-tco 37230 instead. (Contributed by Matthew House, 6-Apr-2026.) (New usage is discouraged.)
∃𝑦(𝑥 ∈ 𝑦 ∧ ∀𝑧(𝑧 ∈ 𝑦 → ∀𝑤(𝑤 ∈ 𝑧 → 𝑤 ∈ 𝑦)))
 
6-Apr-2026el 5406 Any set is an element of some other set. See elALT 5410 for a shorter proof using more axioms, and see elALT2 5331 for a proof that uses ax-9 2155 and ax-pow 5327 instead of ax-pr 5391. (Contributed by NM, 4-Jan-2002.) (Proof shortened by Andrew Salmon, 25-Jul-2011.) Use ax-pr 5391 instead of ax-9 2155 and ax-pow 5327. (Revised by BTernaryTau, 2-Dec-2024.) (Proof shortened by Matthew House, 6-Apr-2026.)
∃𝑦 𝑥 ∈ 𝑦
 
6-Apr-2026axprlem1 5385 Lemma for axpr 5389. There exists a set to which all empty sets belong. (Contributed by Rohan Ridenour, 10-Aug-2023.) (Revised by BJ, 13-Aug-2023.) (Proof shortened by Matthew House, 6-Apr-2026.)
∃𝑥∀𝑦(∀𝑧 ¬ 𝑧 ∈ 𝑦 → 𝑦 ∈ 𝑥)
 
5-Apr-2026nprmmul1 48553 Special factorization of a non-prime integer greater than 3. (Contributed by AV, 5-Apr-2026.)
(𝑁 ∈ (ℤ≥‘4) → (𝑁 ∉ ℙ ↔ ∃𝑎 ∈ (2..^𝑁)∃𝑏 ∈ (2..^𝑁)𝑁 = (𝑎 · 𝑏)))
 
5-Apr-2026nndivides2 48398 Definition of the divides relation for divisors greater than 1. (Contributed by AV, 5-Apr-2026.)
((𝑀 ∈ (2..^𝑁) ∧ 𝑁 ∈ ℕ) → (𝑀 ∥ 𝑁 ↔ ∃𝑛 ∈ (2..^𝑁)(𝑛 · 𝑀) = 𝑁))
 
5-Apr-2026nnmul2b 48345 A factor of a product of integers is at least 2 and less then the product iff the second factor is at least 2 and less then the product. (Contributed by AV, 5-Apr-2026.)
((𝐴 ∈ ℕ ∧ 𝐵 ∈ ℕ ∧ (𝐴 · 𝐵) = 𝑁) → (𝐴 ∈ (2..^𝑁) ↔ 𝐵 ∈ (2..^𝑁)))
 
5-Apr-2026nnmul2 48344 If one factor of a product of integers is at least 2 and less then the product, so is the second factor. (Contributed by AV, 5-Apr-2026.)
((𝐴 ∈ (2..^𝑁) ∧ 𝐵 ∈ ℕ ∧ (𝐴 · 𝐵) = 𝑁) → 𝐵 ∈ (2..^𝑁))
 
5-Apr-2026elfzo2nn 48343 A member of a half-open range of integers starting at 2 is a positive integer. (Contributed by AV, 5-Apr-2026.)
(𝐾 ∈ (2..^𝑁) → 𝐾 ∈ ℕ)
 
5-Apr-2026elfz2nn 48336 A member of a finite set of sequential integers starting at 2 is a positive integer. (Contributed by AV, 5-Apr-2026.)
(𝐾 ∈ (2...𝑁) → 𝐾 ∈ ℕ)
 
5-Apr-2026bj-alrimdh 37464 Deduction form of Theorem 19.21 of [Margaris] p. 90, see 19.21 2244 and 19.21h 2321. (Contributed by NM, 10-Feb-1997.) (Proof shortened by Andrew Salmon, 13-May-2011.) State the most general derivable instance. (Revised by BJ, 5-Apr-2026.)
(𝜑 → ∀𝑥𝜓)    &   (𝜒 → ∀𝑥𝜃)    &   (𝜓 → (𝜃 → 𝜏))    ⇒   (𝜑 → (𝜒 → ∀𝑥𝜏))
 
5-Apr-2026bj-alimdh 37463 General instance of alimdh 1850. (Contributed by NM, 4-Jan-2002.) State the most general derivable instance. (Revised by BJ, 5-Apr-2026.)
(𝜑 → ∀𝑥𝜓)    &   (𝜓 → (𝜒 → 𝜃))    ⇒   (𝜑 → (∀𝑥𝜒 → ∀𝑥𝜃))
 
5-Apr-2026zfrep6 5242 A version of the Axiom of Replacement. Normally 𝜑 would have free variables 𝑥 and 𝑦. Axiom 6 of [Kunen] p. 12. The Separation Scheme ax-sep 5249 cannot be derived from this version and must be stated as a separate axiom in an axiom system (such as Kunen's) that uses this version in place of our ax-rep 5232. (Contributed by NM, 10-Oct-2003.) Shorten proof and reduce axiom dependencies. (Revised by BJ, 5-Apr-2026.)
(∀𝑥 ∈ 𝑧 ∃!𝑦𝜑 → ∃𝑤∀𝑥 ∈ 𝑧 ∃𝑦 ∈ 𝑤 𝜑)
 
5-Apr-2026replem 5241 A lemma for variants of the axiom of replacement: if we can form the set of images of the functional relation, then we can also form a set containing all its images. The converse requires the axiom of separation. (Contributed by BJ, 5-Apr-2026.)
((∀𝑥 ∈ 𝑧 ∃𝑦𝜑 ∧ ∃𝑤∀𝑦(𝑦 ∈ 𝑤 ↔ ∃𝑥 ∈ 𝑧 𝜑)) → ∃𝑤∀𝑥 ∈ 𝑧 ∃𝑦 ∈ 𝑤 𝜑)
 
4-Apr-2026ppi1sum 48660 Value of the prime-counting function pi for 1, according to Ján Mináč. (Contributed by AV, 4-Apr-2026.)
(π‘1) = Σ𝑘 ∈ ∅ (⌊‘((((!‘(𝑘 − 1)) + 1) / 𝑘) − (⌊‘((!‘(𝑘 − 1)) / 𝑘))))
 
4-Apr-2026indprmfz 48659 An indicator function for prime numbers in a finite interval of integers, according to Ján Mináč. (Contributed by AV, 4-Apr-2026.)
𝐼 = (2...𝐴)    ⇒   ((𝟭‘𝐼)‘(𝐼 ∩ ℙ)) = (𝑘 ∈ 𝐼 ↦ (⌊‘((((!‘(𝑘 − 1)) + 1) / 𝑘) − (⌊‘((!‘(𝑘 − 1)) / 𝑘)))))
 
4-Apr-2026indprm 48658 An indicator function for prime numbers, according to Ján Mináč. (Contributed by AV, 4-Apr-2026.)
((𝟭‘(ℤ≥‘2))‘ℙ) = (𝑘 ∈ (ℤ≥‘2) ↦ (⌊‘((((!‘(𝑘 − 1)) + 1) / 𝑘) − (⌊‘((!‘(𝑘 − 1)) / 𝑘)))))
 
4-Apr-2026ppivalnnnprmge6 48655 Value of a term of the prime-counting function pi for positive integers, according to Ján Mináč, for a non-prime number greater than 4. (Contributed by AV, 4-Apr-2026.)
((𝑁 ∈ (ℤ≥‘6) ∧ 𝑁 ∉ ℙ) → (⌊‘((((!‘(𝑁 − 1)) + 1) / 𝑁) − (⌊‘((!‘(𝑁 − 1)) / 𝑁)))) = 0)
 
4-Apr-2026nprmmul3 48555 Special factorization of a non-prime integer greater than 3. (Contributed by AV, 4-Apr-2026.)
(𝑁 ∈ (ℤ≥‘4) → (𝑁 ∉ ℙ ↔ (∃𝑎 ∈ (2..^𝑁)∃𝑏 ∈ (2..^𝑁)(𝑎 < 𝑏 ∧ 𝑁 = (𝑎 · 𝑏)) ∨ ∃𝑎 ∈ (2..^𝑁)𝑁 = (𝑎↑2))))
 
4-Apr-2026rerecne0d 43475 The reciprocal of a nonzero number is nonzero. (Contributed by SN, 4-Apr-2026.)
(𝜑 → 𝐴 ∈ ℝ)    &   (𝜑 → 𝐴 ≠ 0)    ⇒   (𝜑 → (1 /ℝ 𝐴) ≠ 0)
 
4-Apr-2026bj-nnf-cbval 37652 Compared with cbvalv1 2371, this saves ax-12 2213. (Contributed by BJ, 4-Apr-2026.)
(𝜑 → ∀𝑥𝜑)    &   (𝜑 → ∀𝑦𝜑)    &   (𝜑 → Ⅎ'𝑦𝜓)    &   (𝜑 → Ⅎ'𝑥𝜒)    &   ((𝜑 ∧ 𝑥 = 𝑦) → (𝜓 ↔ 𝜒))    ⇒   (𝜑 → (∀𝑥𝜓 ↔ ∀𝑦𝜒))
 
4-Apr-2026bj-nnf-cbvali 37651 Compared with bj-nnf-cbvaliv 37648, replacing the DV condition on 𝑦, 𝜓 with the nonfreeness condition requires ax-11 2194. (Contributed by BJ, 4-Apr-2026.)
(𝜑 → ∀𝑥𝜑)    &   (𝜑 → ∀𝑦𝜑)    &   (𝜑 → Ⅎ'𝑦𝜓)    &   (𝜑 → Ⅎ'𝑥𝜒)    &   ((𝜑 ∧ 𝑥 = 𝑦) → (𝜓 → 𝜒))    ⇒   (𝜑 → (∀𝑥𝜓 → ∀𝑦𝜒))
 
4-Apr-2026bj-nnf-cbvaliv 37648 The only DV conditions are those saying that 𝑦 is a fresh variable used to construct 𝜒. (Contributed by BJ, 4-Apr-2026.)
(𝜑 → ∀𝑥𝜑)    &   (𝜑 → Ⅎ'𝑥𝜒)    &   ((𝜑 ∧ 𝑥 = 𝑦) → (𝜓 → 𝜒))    ⇒   (𝜑 → (∀𝑥𝜓 → ∀𝑦𝜒))
 
4-Apr-2026bj-nnf-spime 37647 An existential generalization result in deduction form, from ax-1 6-- ax-6 2000, where the only DV condition is on 𝑥, 𝑦, and where 𝑥 should be nonfree in the new proposition 𝜒 (and in the context 𝜑). (Contributed by BJ, 4-Apr-2026.)
(𝜑 → ∀𝑥𝜑)    &   (𝜑 → Ⅎ'𝑥𝜓)    &   ((𝜑 ∧ 𝑥 = 𝑦) → (𝜓 → 𝜒))    ⇒   (𝜑 → (𝜓 → ∃𝑥𝜒))
 
4-Apr-2026bj-nnf-spim 37646 A universal specialization result in deduction form, proved from ax-1 6 -- ax-6 2000, where the only DV condition is on 𝑥, 𝑦 and where 𝑥 should be nonfree in the new proposition 𝜒 (and in the context 𝜑). (Contributed by BJ, 4-Apr-2026.)
(𝜑 → ∀𝑥𝜑)    &   (𝜑 → Ⅎ'𝑥𝜒)    &   ((𝜑 ∧ 𝑥 = 𝑦) → (𝜓 → 𝜒))    ⇒   (𝜑 → (∀𝑥𝜓 → 𝜒))
 
4-Apr-2026bj-hbex 37584 A more general instance of hbex 2356. (Contributed by BJ, 4-Apr-2026.)
(𝜑 → ∀𝑥𝜓)    ⇒   (∃𝑦𝜑 → ∀𝑥∃𝑦𝜓)
 
4-Apr-2026bj-hbexd 37582 A more general instance of the deduction form of hbex 2356. (Contributed by BJ, 4-Apr-2026.)
(𝜑 → ∀𝑦𝜓)    &   (𝜓 → (𝜒 → ∀𝑥𝜃))    ⇒   (𝜑 → (∃𝑦𝜒 → ∀𝑥∃𝑦𝜃))
 
4-Apr-2026bj-hbal 37553 More general instance of hbal 2204. (Contributed by BJ, 4-Apr-2026.)
(𝜑 → ∀𝑥𝜓)    ⇒   (∀𝑦𝜑 → ∀𝑥∀𝑦𝜓)
 
4-Apr-2026bj-hbald 37551 General statement that hbald 2205 proves . (Contributed by BJ, 4-Apr-2026.)
(𝜑 → ∀𝑦𝜓)    &   (𝜓 → (𝜒 → ∀𝑥𝜃))    ⇒   (𝜑 → (∀𝑦𝜒 → ∀𝑥∀𝑦𝜃))
 
4-Apr-2026bj-spim0 37538 A universal specialization result in deduction form, proved from ax-1 6 -- ax-6 2000, where the only DV condition is on 𝑥, 𝑦 and where 𝑥 should be nonfree in the new proposition 𝜒 (and in the context 𝜑). (Contributed by BJ, 4-Apr-2026.)
(𝜑 → ∀𝑥𝜑)    &   (𝜑 → (∃𝑥𝜒 → 𝜒))    &   ((𝜑 ∧ 𝑥 = 𝑦) → (𝜓 → 𝜒))    ⇒   (𝜑 → (∀𝑥𝜓 → 𝜒))
 
4-Apr-2026bj-cbveximdv 37503 A lemma for alpha-renaming of variables bound by an existential quantifier. (Contributed by BJ, 4-Apr-2026.) (Proof modification is discouraged.)
(𝜑 → ∀𝑥𝜑)    &   (𝜑 → ∀𝑦𝜑)    &   (𝜑 → (𝜒 → ∀𝑦𝜒))    &   (𝜑 → ∀𝑥∃𝑦𝜓)    &   ((𝜑 ∧ 𝜓) → (𝜒 → 𝜃))    ⇒   (𝜑 → (∃𝑥𝜒 → ∃𝑦𝜃))
 
4-Apr-2026bj-cbvalimdv 37502 A lemma for alpha-renaming of variables bound by a universal quantifier. (Contributed by BJ, 4-Apr-2026.) (Proof modification is discouraged.)
(𝜑 → ∀𝑥𝜑)    &   (𝜑 → ∀𝑦𝜑)    &   (𝜑 → (∃𝑥𝜃 → 𝜃))    &   (𝜑 → ∀𝑦∃𝑥𝜓)    &   ((𝜑 ∧ 𝜓) → (𝜒 → 𝜃))    ⇒   (𝜑 → (∀𝑥𝜒 → ∀𝑦𝜃))
 
4-Apr-2026bj-cbveximd 37501 A lemma for alpha-renaming of variables bound by an existential quantifier. (Contributed by BJ, 4-Apr-2026.) (Proof modification is discouraged.)
(𝜑 → ∀𝑥𝜑)    &   (𝜑 → ∀𝑦𝜑)    &   (𝜑 → (𝜒 → ∀𝑦𝜒))    &   (𝜑 → (∃𝑥𝜃 → 𝜃))    &   (𝜑 → ∀𝑥∃𝑦𝜓)    &   ((𝜑 ∧ 𝜓) → (𝜒 → 𝜃))    ⇒   (𝜑 → (∃𝑥𝜒 → ∃𝑦𝜃))
 
4-Apr-2026bj-cbvalimd 37500 A lemma for alpha-renaming of variables bound by a universal quantifier. (Contributed by BJ, 4-Apr-2026.) (Proof modification is discouraged.)
(𝜑 → ∀𝑥𝜑)    &   (𝜑 → ∀𝑦𝜑)    &   (𝜑 → (𝜒 → ∀𝑦𝜒))    &   (𝜑 → (∃𝑥𝜃 → 𝜃))    &   (𝜑 → ∀𝑦∃𝑥𝜓)    &   ((𝜑 ∧ 𝜓) → (𝜒 → 𝜃))    ⇒   (𝜑 → (∀𝑥𝜒 → ∀𝑦𝜃))
 
4-Apr-2026bj-cbvalimd0 37497 A lemma for alpha-renaming of variables bound by a universal quantifier. In applications, 𝑥 = 𝑦 will be substituted for 𝜓 and ax6ev 2002 will prove Hypothesis bj-cbvalimd0.denote. When ax6ev 2002 is not available but only its universal closure is, then bj-cbvalimd 37500 or bj-cbvalimdv 37502 should be used (see bj-cbvalimdlem 37498, bj-cbval 37515). (Contributed by BJ, 4-Apr-2026.)
(𝜑 → ∀𝑥𝜑)    &   (𝜑 → ∀𝑦𝜑)    &   (𝜑 → (𝜒 → ∀𝑦𝜒))    &   (𝜑 → (∃𝑥𝜃 → 𝜃))    &   (𝜑 → ∃𝑥𝜓)    &   ((𝜑 ∧ 𝜓) → (𝜒 → 𝜃))    ⇒   (𝜑 → (∀𝑥𝜒 → ∀𝑦𝜃))
 
4-Apr-2026bj-spime 37496 A lemma for existential generalization. In applications, 𝑥 = 𝑦 will be substituted for 𝜓 and ax6ev 2002 will prove Hypothesis bj-spime.denote. (Contributed by BJ, 4-Apr-2026.)
(𝜑 → ∀𝑥𝜑)    &   (𝜑 → (𝜒 → ∀𝑥𝜒))    &   (𝜑 → ∃𝑥𝜓)    &   ((𝜑 ∧ 𝜓) → (𝜒 → 𝜃))    ⇒   (𝜑 → (𝜒 → ∃𝑥𝜃))
 
4-Apr-2026bj-spim 37495 A lemma for universal specification. In applications, 𝑥 = 𝑦 will be substituted for 𝜓 and ax6ev 2002 will prove Hypothesis bj-spim.denote. (Contributed by BJ, 4-Apr-2026.)
(𝜑 → ∀𝑥𝜑)    &   (𝜑 → (∃𝑥𝜃 → 𝜃))    &   (𝜑 → ∃𝑥𝜓)    &   ((𝜑 ∧ 𝜓) → (𝜒 → 𝜃))    ⇒   (𝜑 → (∀𝑥𝜒 → 𝜃))
 
3-Apr-2026bj-spimenfa 37494 An existential generalization result: if 𝜑 holds and implies 𝜓 for at least one value of 𝑥, and if furthermore 𝑥 is ∀ -weakly nonfree in 𝜑, then 𝜓 holds for at least one value of 𝑥. (Contributed by BJ, 3-Apr-2026.) Proof should not use 19.35 1910. (Proof modification is discouraged.)
((𝜑 → ∀𝑥𝜑) → (∃𝑥(𝜑 → 𝜓) → (𝜑 → ∃𝑥𝜓)))
 
3-Apr-2026bj-spimnfe 37493 A universal specification result: if 𝜑 is true for all values of 𝑥 and implies 𝜓 for at least one value, and if furthermore 𝑥 is ∃-weakly nonfree in 𝜓, then 𝜓 follows. An intermediate result on the way to prove 19.36i 2268, bj-19.36im 37635, 19.36imv 1978, spimfw 1998... (Contributed by BJ, 3-Apr-2026.) Proof should not use 19.35 1910. (Proof modification is discouraged.)
((∃𝑥𝜓 → 𝜓) → (∃𝑥(𝜑 → 𝜓) → (∀𝑥𝜑 → 𝜓)))
 
3-Apr-2026bj-imim11i 37389 The propositional function ((. → 𝜑) → 𝜓) is increasing. Its associated inference is wl-syls2 38409. (Contributed by BJ, 3-Apr-2026.)
(𝜑 → 𝜓)    ⇒   (((𝜑 → 𝜒) → 𝜃) → ((𝜓 → 𝜒) → 𝜃))
 
3-Apr-2026bj-imim11 37388 The propositional function ((. → 𝜑) → 𝜓) is increasing. (Contributed by BJ, 3-Apr-2026.)
((𝜑 → 𝜓) → (((𝜑 → 𝜒) → 𝜃) → ((𝜓 → 𝜒) → 𝜃)))
 
2-Apr-2026hoicvr 47502 𝐼 is a countable set of half-open intervals that covers the whole multidimensional reals. See Definition 1135 (b) of [Fremlin1] p. 29. (Contributed by Glauco Siliprandi, 11-Oct-2020.) Avoid ax-rep 5232 and shorten proof. (Revised by GG, 2-Apr-2026.)
𝐼 = (𝑗 ∈ ℕ ↦ (𝑥 ∈ 𝑋 ↦ ⟨-𝑗, 𝑗⟩))    &   (𝜑 → 𝑋 ∈ Fin)    ⇒   (𝜑 → (ℝ ↑m 𝑋) ⊆ ∪ 𝑗 ∈ ℕ X𝑖 ∈ 𝑋 (([,) ∘ (𝐼‘𝑗))‘𝑖))
 
2-Apr-2026rerecrecd 43478 A number is equal to the reciprocal of its reciprocal. (Contributed by SN, 2-Apr-2026.)
(𝜑 → 𝐴 ∈ ℝ)    &   (𝜑 → 𝐴 ≠ 0)    ⇒   (𝜑 → (1 /ℝ (1 /ℝ 𝐴)) = 𝐴)
 
2-Apr-2026sn-redividd 43473 A number divided by itself is 1. (Contributed by SN, 2-Apr-2026.)
(𝜑 → 𝐴 ∈ ℝ)    &   (𝜑 → 𝐴 ≠ 0)    ⇒   (𝜑 → (𝐴 /ℝ 𝐴) = 1)
 
2-Apr-2026sn-rediv0d 43472 Division into zero is zero. (Contributed by SN, 2-Apr-2026.)
(𝜑 → 𝐴 ∈ ℝ)    &   (𝜑 → 𝐴 ≠ 0)    ⇒   (𝜑 → (0 /ℝ 𝐴) = 0)
 
2-Apr-2026sn-rediv1d 43471 A number divided by 1 is itself. (Contributed by SN, 2-Apr-2026.)
(𝜑 → 𝐴 ∈ ℝ)    ⇒   (𝜑 → (𝐴 /ℝ 1) = 𝐴)
 
2-Apr-2026rediveq1d 43470 Equality in terms of unit ratio. (Contributed by SN, 2-Apr-2026.)
(𝜑 → 𝐴 ∈ ℝ)    &   (𝜑 → 𝐵 ∈ ℝ)    &   (𝜑 → 𝐵 ≠ 0)    ⇒   (𝜑 → ((𝐴 /ℝ 𝐵) = 1 ↔ 𝐴 = 𝐵))
 
2-Apr-2026redivne0bd 43469 The ratio of nonzero numbers is nonzero. (Contributed by SN, 2-Apr-2026.)
(𝜑 → 𝐴 ∈ ℝ)    &   (𝜑 → 𝐵 ∈ ℝ)    &   (𝜑 → 𝐵 ≠ 0)    ⇒   (𝜑 → (𝐴 ≠ 0 ↔ (𝐴 /ℝ 𝐵) ≠ 0))
 
2-Apr-2026redivmul2d 43465 Relationship between division and multiplication. (Contributed by SN, 2-Apr-2026.)
(𝜑 → 𝐴 ∈ ℝ)    &   (𝜑 → 𝐵 ∈ ℝ)    &   (𝜑 → 𝐶 ∈ ℝ)    &   (𝜑 → 𝐶 ≠ 0)    ⇒   (𝜑 → ((𝐴 /ℝ 𝐶) = 𝐵 ↔ 𝐴 = (𝐶 · 𝐵)))
 
2-Apr-2026padct 33292 Index a countable set with integers and pad with 𝑍. (Contributed by Thierry Arnoux, 1-Jun-2020.) Avoid ax-rep 5232. (Revised by GG, 2-Apr-2026.)
((𝐴 ≼ ω ∧ 𝑍 ∈ 𝑉 ∧ ¬ 𝑍 ∈ 𝐴) → ∃𝑓(𝑓:ℕ⟶(𝐴 ∪ {𝑍}) ∧ 𝐴 ⊆ ran 𝑓 ∧ Fun (◡𝑓 ↾ 𝐴)))
 
2-Apr-2026istrkg2ld 28904 Property of fulfilling the lower dimension 2 axiom. (Contributed by Thierry Arnoux, 20-Nov-2019.) Avoid ax-rep 5232. (Revised by GG, 2-Apr-2026.)
𝑃 = (Base‘𝐺)    &    − = (dist‘𝐺)    &   𝐼 = (Itv‘𝐺)    ⇒   (𝐺 ∈ 𝑉 → (𝐺DimTarskiG≥2 ↔ ∃𝑥 ∈ 𝑃 ∃𝑦 ∈ 𝑃 ∃𝑧 ∈ 𝑃 ¬ (𝑧 ∈ (𝑥𝐼𝑦) ∨ 𝑥 ∈ (𝑧𝐼𝑦) ∨ 𝑦 ∈ (𝑥𝐼𝑧))))
 
2-Apr-2026smndex1igid 19082 The composition of the modulo function 𝐼 and a constant function (𝐺‘𝐾) results in (𝐺‘𝐾) itself. (Contributed by AV, 14-Feb-2024.) Avoid ax-rep 5232. (Revised by GG, 2-Apr-2026.)
𝑀 = (EndoFMnd‘ℕ0)    &   𝑁 ∈ ℕ    &   𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁))    &   𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛))    ⇒   (𝐾 ∈ (0..^𝑁) → (𝐼 ∘ (𝐺‘𝐾)) = (𝐺‘𝐾))
 
2-Apr-2026smndex1gid 19080 The composition of a constant function (𝐺‘𝐾) with another endofunction on ℕ0 results in (𝐺‘𝐾) itself. (Contributed by AV, 14-Feb-2024.) Avoid ax-rep 5232. (Revised by GG, 2-Apr-2026.)
𝑀 = (EndoFMnd‘ℕ0)    &   𝑁 ∈ ℕ    &   𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁))    &   𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛))    ⇒   ((𝐹 ∈ (Base‘𝑀) ∧ 𝐾 ∈ (0..^𝑁)) → ((𝐺‘𝐾) ∘ 𝐹) = (𝐺‘𝐾))
 
2-Apr-2026smndex1gbas 19078 The constant functions (𝐺‘𝐾) are endofunctions on ℕ0. (Contributed by AV, 12-Feb-2024.) Avoid ax-rep 5232 and shorten proof. (Revised by GG, 2-Apr-2026.)
𝑀 = (EndoFMnd‘ℕ0)    &   𝑁 ∈ ℕ    &   𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁))    &   𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛))    ⇒   (𝐾 ∈ (0..^𝑁) → (𝐺‘𝐾) ∈ (Base‘𝑀))
 
1-Apr-2026nowisdomv 31057 One's wisdom on matters of the universe can be refuted on April Fool's day. (Contributed by Prof. Loof Lirpa, 1-Apr-2026.) (New usage is discouraged.)
¬ 𝑊⟨“ I 5”⟩dom V
 
28-Mar-2026copsex2gd 38027 Implicit substitution inference for ordered pairs. (Contributed by NM, 28-May-1995.) Use a similar proof to copsex4g 5467 to reduce axiom usage. (Revised by SN, 1-Sep-2024.) Adapt copsex2g 5465 $p to deduction form. (Revised by BJ, 28-Mar-2026.) Do not use copsex2g 5465. (Proof modification is discouraged.)
((𝜑 ∧ (𝑥 = 𝐴 ∧ 𝑦 = 𝐵)) → (𝜓 ↔ 𝜒))    ⇒   ((𝜑 ∧ (𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑊)) → (∃𝑥∃𝑦(⟨𝐴, 𝐵⟩ = ⟨𝑥, 𝑦⟩ ∧ 𝜓) ↔ 𝜒))
 
28-Mar-2026cgsex2gd 38026 Implicit substitution inference for general classes. (Contributed by NM, 26-Jul-1995.) Adapt cgsex2g 3496 to deduction form. (Revised by BJ, 28-Mar-2026.) Do not use cgsex2g 3496. (Proof modification is discouraged.)
((𝜑 ∧ (𝑥 = 𝐴 ∧ 𝑦 = 𝐵)) → 𝜓)    &   ((𝜑 ∧ 𝜓) → (𝜒 ↔ 𝜃))    ⇒   ((𝜑 ∧ (𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑊)) → (∃𝑥∃𝑦(𝜓 ∧ 𝜒) ↔ 𝜃))
 
28-Mar-2026bj-alnnf2 37610 If a proposition holds, then it holds for all values of a given variable if and only if it does not depend on that variable. (Contributed by BJ, 28-Mar-2026.)
(𝜑 → (∀𝑥𝜑 ↔ Ⅎ'𝑥𝜑))
 
28-Mar-2026bj-alnnf 37609 In deduction-style proofs, it is equivalent to assert that the context holds for all values of a variable, or that is does not depend on that variable. (Contributed by BJ, 28-Mar-2026.)
((𝜑 → ∀𝑥𝜑) ↔ (𝜑 → Ⅎ'𝑥𝜑))
 
28-Mar-2026bj-alsyl 37461 Syllogism under the universal quantifier, in the curried form appearing as Theorem *10.3 of [WhiteheadRussell] p. 145. See alsyl 1926 for the uncurried form. (Contributed by BJ, 28-Mar-2026.)
(∀𝑥(𝜑 → 𝜓) → (∀𝑥(𝜓 → 𝜒) → ∀𝑥(𝜑 → 𝜒)))
 
27-Mar-2026axnulALT2 35694 Alternate proof of axnul 5259, proved from propositional calculus, ax-gen 1828, ax-4 1842, ax-6 2000, and ax-rep 5232. (Proof modification is discouraged.) (New usage is discouraged.) (Contributed by BTernaryTau, 27-Mar-2026.)
∃𝑥∀𝑦 ¬ 𝑦 ∈ 𝑥
 
26-Mar-2026axprALT2 35713 Alternate proof of axpr 5389, proved from predicate calculus, ax-rep 5232, and ax-inf2 9626. (Contributed by BTernaryTau, 26-Mar-2026.) (Proof modification is discouraged.) (New usage is discouraged.)
∃𝑧∀𝑤((𝑤 = 𝑥 ∨ 𝑤 = 𝑦) → 𝑤 ∈ 𝑧)
 
21-Mar-2026bj-nnfbd0 37620 If two formulas are equivalent, then nonfreeness of a variable in one of them is equivalent to nonfreeness in the other, deduction form. The antecedent of the conclusion is in the "strong necessity" modality of modal logic (see also bj-nnftht 37615) in order not to require sp 2220 (modal T). See bj-nnfbi 37619. (Contributed by BJ, 21-Mar-2026.)
(𝜑 → (𝜓 ↔ 𝜒))    ⇒   ((𝜑 ∧ ∀𝑥𝜑) → (Ⅎ'𝑥𝜓 ↔ Ⅎ'𝑥𝜒))
 
20-Mar-2026bj-bisimpr 37393 Implication from equivalence with a conjunct. Its associated inference is simprbi 503. (Contributed by BJ, 20-Mar-2026.)
((𝜑 ↔ (𝜓 ∧ 𝜒)) → (𝜑 → 𝜒))
 
20-Mar-2026bj-bisimpl 37392 Implication from equivalence with a conjunct. Its associated inference is simplbi 502. (Contributed by BJ, 20-Mar-2026.)
((𝜑 ↔ (𝜓 ∧ 𝜒)) → (𝜑 → 𝜓))
 
19-Mar-2026bj-almpig 37460 A partially quantified form of mpi 21 similar to bj-almpi 37459. (Contributed by BJ, 19-Mar-2026.)
(𝜑 → (𝜒 → 𝜓))    &   ∀𝑥𝜒    ⇒   ∀𝑥(𝜑 → 𝜓)
 
19-Mar-2026bj-almpi 37459 A quantified form of mpi 21. See also barbara 2688, bj-ala1i 37458, bj-almp 37451. (Contributed by BJ, 19-Mar-2026.)
∀𝑥(𝜑 → (𝜒 → 𝜓))    &   ∀𝑥𝜒    ⇒   ∀𝑥(𝜑 → 𝜓)
 
19-Mar-2026bj-alimii 37457 Inference associated with alimi 1844. Double inference associated with alim 1843. The usual proof of an associated inference (here from alimi 1844 and ax-mp 5) has the same size and same number of steps. (Contributed by BJ, 19-Mar-2026.)
(𝜓 → 𝜑)    &   ∀𝑥𝜓    ⇒   ∀𝑥𝜑
 
19-Mar-2026bj-almp 37451 A quantified form of ax-mp 5. See also barbara 2688, bj-ala1i 37458, bj-almpi 37459. (Contributed by BJ, 19-Mar-2026.)
∀𝑥(𝜓 → 𝜑)    &   ∀𝑥𝜓    ⇒   ∀𝑥𝜑
 
17-Mar-2026bj-evalf 37963 The evaluation at a class is a function from the universal class into the universal class. (Contributed by BJ, 17-Mar-2026.)
Slot 𝐴:V⟶V
 
16-Mar-2026sin5tlem1 47863 Lemma 1 for quintupled angle sine calculation, expanding triple-angle sine times double-angle cosine. (Contributed by Ender Ting, 16-Mar-2026.)
(𝑁 ∈ ℂ → (((3 · 𝑁) − (4 · (𝑁↑3))) · (1 − (2 · (𝑁↑2)))) = (((8 · (𝑁↑5)) − (10 · (𝑁↑3))) + (3 · 𝑁)))
 
16-Mar-2026cos3t 47862 Triple-angle formula for cosine, in pure cosine form. (Contributed by Ender Ting, 16-Mar-2026.)
(𝐴 ∈ ℂ → (cos‘(3 · 𝐴)) = ((4 · ((cos‘𝐴)↑3)) − (3 · (cos‘𝐴))))
 
16-Mar-2026sin3t 47861 Triple-angle formula for sine, in pure sine form. (Contributed by Ender Ting, 16-Mar-2026.)
(𝐴 ∈ ℂ → (sin‘(3 · 𝐴)) = ((3 · (sin‘𝐴)) − (4 · ((sin‘𝐴)↑3))))
 
16-Mar-2026esplyfvaln 34188 The last elementary symmetric polynomial is the product of all variables. (Contributed by Thierry Arnoux, 16-Mar-2026.)
𝑊 = (𝐼 mPoly 𝑅)    &   𝑉 = (𝐼 mVar 𝑅)    &   𝐸 = (𝐼eSymPoly𝑅)    &   (𝜑 → 𝐼 ∈ Fin)    &   (𝜑 → 𝑅 ∈ CRing)    &   𝑁 = (♯‘𝐼)    &   𝑀 = (mulGrp‘𝑊)    ⇒   (𝜑 → (𝐸‘𝑁) = (𝑀 Σg 𝑉))
 
16-Mar-2026esplyfval1 34187 The first elementary symmetric polynomial is the sum of all variables. (Contributed by Thierry Arnoux, 16-Mar-2026.)
𝑊 = (𝐼 mPoly 𝑅)    &   𝑉 = (𝐼 mVar 𝑅)    &   𝐸 = (𝐼eSymPoly𝑅)    &   (𝜑 → 𝐼 ∈ Fin)    &   (𝜑 → 𝑅 ∈ Ring)    ⇒   (𝜑 → (𝐸‘1) = (𝑊 Σg 𝑉))
 
16-Mar-2026mplmonprod 34168 Finite product of monomials. Here the function 𝐺 maps a bag of variables to the corresponding monomial. (Contributed by Thierry Arnoux, 16-Mar-2026.)
𝑃 = (𝐼 mPoly 𝑅)    &   𝐵 = (Base‘𝑃)    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝐼 ∈ 𝑉)    &   𝐷 = {ℎ ∈ (ℕ0 ↑m 𝐼) ∣ ℎ finSupp 0}    &   (𝜑 → 𝐴 ∈ Fin)    &   (𝜑 → 𝐹:𝐴⟶𝐷)    &    1 = (1r‘𝑅)    &    0 = (0g‘𝑅)    &   𝑀 = (mulGrp‘𝑃)    &   𝐺 = (𝑦 ∈ 𝐷 ↦ (𝑧 ∈ 𝐷 ↦ if(𝑧 = 𝑦, 1 , 0 )))    ⇒   (𝜑 → (𝑀 Σg (𝐺 ∘ 𝐹)) = (𝐺‘(𝑖 ∈ 𝐼 ↦ (ℂfld Σg (𝑥 ∈ 𝐴 ↦ ((𝐹‘𝑥)‘𝑖))))))
 
16-Mar-2026mplgsum 34167 Finite commutative sums of polynomials are taken componentwise. (Contributed by Thierry Arnoux, 16-Mar-2026.)
𝑃 = (𝐼 mPoly 𝑅)    &   𝐵 = (Base‘𝑃)    &   (𝜑 → 𝑅 ∈ Ring)    &   (𝜑 → 𝐼 ∈ 𝑉)    &   𝐷 = {ℎ ∈ (ℕ0 ↑m 𝐼) ∣ ℎ finSupp 0}    &   (𝜑 → 𝐴 ∈ Fin)    &   (𝜑 → 𝐹:𝐴⟶𝐵)    ⇒   (𝜑 → (𝑃 Σg 𝐹) = (𝑦 ∈ 𝐷 ↦ (𝑅 Σg (𝑘 ∈ 𝐴 ↦ ((𝐹‘𝑘)‘𝑦)))))
 
16-Mar-2026psrmonprod 34166 Finite product of bags of variables in a power series. Here the function 𝐺 maps a bag of variables to the corresponding monomial. (Contributed by Thierry Arnoux, 16-Mar-2026.)
𝑆 = (𝐼 mPwSer 𝑅)    &   𝐵 = (Base‘𝑆)    &   (𝜑 → 𝑅 ∈ CRing)    &   (𝜑 → 𝐼 ∈ 𝑉)    &   𝐷 = {ℎ ∈ (ℕ0 ↑m 𝐼) ∣ ℎ finSupp 0}    &   (𝜑 → 𝐴 ∈ Fin)    &   (𝜑 → 𝐹:𝐴⟶𝐷)    &    1 = (1r‘𝑅)    &    0 = (0g‘𝑅)    &   𝑀 = (mulGrp‘𝑆)    &   𝐺 = (𝑦 ∈ 𝐷 ↦ (𝑧 ∈ 𝐷 ↦ if(𝑧 = 𝑦, 1 , 0 )))    ⇒   (𝜑 → (𝑀 Σg (𝐺 ∘ 𝐹)) = (𝐺‘(𝑖 ∈ 𝐼 ↦ (ℂfld Σg (𝑥 ∈ 𝐴 ↦ ((𝐹‘𝑥)‘𝑖))))))
 
16-Mar-2026psrmonmul2 34165 The product of two power series monomials adds the exponent vectors together. Here, the function 𝐺 is a monomial builder, which maps a bag of variables with the monic monomial with only those variables. (Contributed by Thierry Arnoux, 16-Mar-2026.)
𝑆 = (𝐼 mPwSer 𝑅)    &   𝐵 = (Base‘𝑆)    &    0 = (0g‘𝑅)    &    1 = (1r‘𝑅)    &   𝐷 = {ℎ ∈ (ℕ0 ↑m 𝐼) ∣ ℎ finSupp 0}    &   (𝜑 → 𝐼 ∈ 𝑊)    &   (𝜑 → 𝑅 ∈ Ring)    &   (𝜑 → 𝑋 ∈ 𝐷)    &    · = (.r‘𝑆)    &   (𝜑 → 𝑌 ∈ 𝐷)    &   𝐺 = (𝑦 ∈ 𝐷 ↦ (𝑧 ∈ 𝐷 ↦ if(𝑧 = 𝑦, 1 , 0 )))    ⇒   (𝜑 → ((𝐺‘𝑋) · (𝐺‘𝑌)) = (𝐺‘(𝑋 ∘f + 𝑌)))
 
16-Mar-2026psrmonmul 34164 The product of two power series monomials adds the exponent vectors together. For example, the product of (𝑥↑2)(𝑦↑2) with (𝑦↑1)(𝑧↑3) is (𝑥↑2)(𝑦↑3)(𝑧↑3), where the exponent vectors ⟨2, 2, 0⟩ and ⟨0, 1, 3⟩ are added to give ⟨2, 3, 3⟩. (Contributed by Thierry Arnoux, 16-Mar-2026.)
𝑆 = (𝐼 mPwSer 𝑅)    &   𝐵 = (Base‘𝑆)    &    0 = (0g‘𝑅)    &    1 = (1r‘𝑅)    &   𝐷 = {ℎ ∈ (ℕ0 ↑m 𝐼) ∣ ℎ finSupp 0}    &   (𝜑 → 𝐼 ∈ 𝑊)    &   (𝜑 → 𝑅 ∈ Ring)    &   (𝜑 → 𝑋 ∈ 𝐷)    &    · = (.r‘𝑆)    &   (𝜑 → 𝑌 ∈ 𝐷)    ⇒   (𝜑 → ((𝑦 ∈ 𝐷 ↦ if(𝑦 = 𝑋, 1 , 0 )) · (𝑦 ∈ 𝐷 ↦ if(𝑦 = 𝑌, 1 , 0 ))) = (𝑦 ∈ 𝐷 ↦ if(𝑦 = (𝑋 ∘f + 𝑌), 1 , 0 )))
 
16-Mar-2026psrmon 34163 A monomial is a power series. (Contributed by Thierry Arnoux, 16-Mar-2026.)
𝑆 = (𝐼 mPwSer 𝑅)    &   𝐵 = (Base‘𝑆)    &    0 = (0g‘𝑅)    &    1 = (1r‘𝑅)    &   𝐷 = {ℎ ∈ (ℕ0 ↑m 𝐼) ∣ ℎ finSupp 0}    &   (𝜑 → 𝐼 ∈ 𝑊)    &   (𝜑 → 𝑅 ∈ Ring)    &   (𝜑 → 𝑋 ∈ 𝐷)    ⇒   (𝜑 → (𝑦 ∈ 𝐷 ↦ if(𝑦 = 𝑋, 1 , 0 )) ∈ 𝐵)
 
16-Mar-2026psrgsum 34162 Finite commutative sums of power series are taken componentwise. (Contributed by Thierry Arnoux, 16-Mar-2026.)
𝑆 = (𝐼 mPwSer 𝑅)    &   𝐵 = (Base‘𝑆)    &   (𝜑 → 𝑅 ∈ Ring)    &   (𝜑 → 𝐼 ∈ 𝑉)    &   𝐷 = {ℎ ∈ (ℕ0 ↑m 𝐼) ∣ ℎ finSupp 0}    &   (𝜑 → 𝐴 ∈ Fin)    &   (𝜑 → 𝐹:𝐴⟶𝐵)    ⇒   (𝜑 → (𝑆 Σg 𝐹) = (𝑦 ∈ 𝐷 ↦ (𝑅 Σg (𝑘 ∈ 𝐴 ↦ ((𝐹‘𝑘)‘𝑦)))))
 
16-Mar-2026suppgsumssiun 33615 The support of a function defined as a group sum is a subset of the indexed union of the supports. (Contributed by Thierry Arnoux, 16-Mar-2026.)
𝑍 = (0g‘𝑀)    &   (𝜑 → 𝑀 ∈ Mnd)    &   (𝜑 → 𝐵 ∈ 𝑊)    &   (𝜑 → 𝐴 ∈ 𝑉)    &   (((𝜑 ∧ 𝑥 ∈ 𝐴) ∧ 𝑦 ∈ 𝐵) → 𝐶 ∈ 𝑋)    ⇒   (𝜑 → ((𝑥 ∈ 𝐴 ↦ (𝑀 Σg (𝑦 ∈ 𝐵 ↦ 𝐶))) supp 𝑍) ⊆ ∪ 𝑦 ∈ 𝐵 ((𝑥 ∈ 𝐴 ↦ 𝐶) supp 𝑍))
 
15-Mar-2026goldrasin 47873 Alternative trigonometric formula for the golden ratio. (Contributed by Ender Ting, 15-Mar-2026.)
𝐹 = (2 · (cos‘(π / 5)))    ⇒   𝐹 = (2 · (sin‘(π · (3 / 10))))
 
15-Mar-2026goldrarr 47872 The golden ratio is a real value. (Contributed by Ender Ting, 15-Mar-2026.)
𝐹 = (2 · (cos‘(π / 5)))    ⇒   𝐹 ∈ ℝ
 
14-Mar-2026bj-axreprepsep 37959 Strong axiom of replacement (universal closure of ax-rep 5232) from the axioms of separation and replacement as written in the theorem's hypotheses.

The statement does not require a nonempty universe; most of the proof does not either, except for the use of 19.8a 2218, which could be removed by reworking the proof, since it is applied in a subexpression bound by the variable it introduces. Proof modifications should not introduce steps relying on a nonempty universe, like alrimiv 1960. (Contributed by BJ, 14-Mar-2026.) (Proof modification is discouraged.)

∀𝑥∃𝑠∀𝑦(𝑦 ∈ 𝑠 ↔ (𝑦 ∈ 𝑥 ∧ ∃𝑧𝜑))    &   ∀𝑠(∀𝑦 ∈ 𝑠 ∃!𝑧𝜑 → ∃𝑡∀𝑧(𝑧 ∈ 𝑡 ↔ ∃𝑦 ∈ 𝑠 𝜑))    ⇒   ∀𝑥(∀𝑦 ∈ 𝑥 ∃*𝑧𝜑 → ∃𝑡∀𝑧(𝑧 ∈ 𝑡 ↔ ∃𝑦 ∈ 𝑥 𝜑))
 
14-Mar-2026bj-axseprep 37958 Axiom of separation (universal closure of ax-sep 5249) from a weak form of the axiom of replacement requiring that the functional relation in it be a (total) function and the weak emptyset axiom (existence of an empty set provided existence of a set), as written in the theorem's hypotheses.

This result shows that the weak emptyset axiom is not only the result of a cheap way to avoid an axiom redundancy (in this case, the existence axiom extru 2008) by adding it as an antecedent, but also permits to prove nontrivial results that hold in nonnecessarily nonempty universes.

This proof is by cases so is not intuitionistic. The statement does not require a nonempty universe; most of the proof does not either, and the parts that do (e.g., near sb8ef 2385 and sbequ12r 2288 and eueq2 3668) could be reworked to avoid it. Proof modifications should not introduce steps relying on a nonempty universe, like alrimiv 1960. (Contributed by BJ, 14-Mar-2026.) (Proof modification is discouraged.)

(∃𝑥⊤ → ∃𝑦∀𝑧 ∈ 𝑦 ⊥)    &   ∀𝑥(∀𝑧 ∈ 𝑥 ∃!𝑡𝜓 → ∃𝑦∀𝑡(𝑡 ∈ 𝑦 ↔ ∃𝑧 ∈ 𝑥 𝜓))    &   (𝜓 ↔ ((𝜑 ∧ 𝑡 = 𝑧) ∨ (¬ 𝜑 ∧ 𝑡 = 𝑎)))    ⇒   ∀𝑥∃𝑦∀𝑧(𝑧 ∈ 𝑦 ↔ (𝑧 ∈ 𝑥 ∧ 𝜑))
 
14-Mar-2026bj-rep 37957 Version of the axiom of replacement requiring the functional relation in the axiom to be a (total) function from ax-rep 5232 (in the form of axrep6 5240). (Contributed by BJ, 14-Mar-2026.) The proof proves the statement without the DV condition on 𝑥, 𝜑, but the DV condition is added to this statement to show that this weaker version is sufficient. (Proof modification is discouraged.) (New usage is discouraged.)
∀𝑥(∀𝑦 ∈ 𝑥 ∃!𝑧𝜑 → ∃𝑡∀𝑧(𝑧 ∈ 𝑡 ↔ ∃𝑦 ∈ 𝑥 𝜑))
 
14-Mar-2026bj-cbvaew 37513 Exixtentially quantifying over a non-occurring variable is independent from the variable, under a weaker condition than in bj-cbvexvv 37509. (Contributed by BJ, 14-Mar-2026.) (Proof modification is discouraged.)
((∀𝑥𝜑 → ∀𝑦⊥) → (∃𝑦𝜓 → ∃𝑥𝜓))
 
14-Mar-2026bj-cbveaw 37512 Universally quantifying over a non-occurring variable is independent from the variable, under a weaker condition than in bj-cbvalvv 37508. (Contributed by BJ, 14-Mar-2026.) (Proof modification is discouraged.)
((∃𝑥⊤ → ∃𝑦𝜑) → (∀𝑦𝜓 → ∀𝑥𝜓))
 
14-Mar-2026bj-cbvew 37511 Existentially quantifying over a non-occurring variable is independent from the variable, under a weaker condition than in bj-cbvexvv 37509. If ⊤ is substituted for 𝜑, then the statement reads: "existentially quantifying over a non-occurring variable is independent from the variable as soon as that result is true for the True truth constant. The label "cbvew" means "'change bound variable' theorem, 'exists' quantifier, weak version". (Contributed by BJ, 14-Mar-2026.) This proof is intuitionistic. (Proof modification is discouraged.)
((∃𝑥⊤ → ∃𝑦𝜑) → (∃𝑥𝜓 → ∃𝑦𝜓))
 
14-Mar-2026bj-cbvaw 37510 Universally quantifying over a non-occurring variable is independent from the variable, under a weaker condition than in bj-cbvalvv 37508. If ⊥ is substituted for 𝜑, then the statement reads: "universally quantifying over a non-occurring variable is independent from the variable as soon as that result is true for the False truth constant". The label "cbvaw" means "'change bound variable' theorem, 'all' quantifier, weak version". (Contributed by BJ, 14-Mar-2026.) This proof is not intuitionistic (it uses ja 188); an intuitionistically valid statement is obtained by expressing the antecedent as a disjunction (classically equivalent through imor 867). (Proof modification is discouraged.)
((∀𝑥𝜑 → ∀𝑦⊥) → (∀𝑥𝜓 → ∀𝑦𝜓))
 
14-Mar-2026bj-exextruan 37507 An equivalent expression for existential quantification over a non-occurring variable proved over ax-1 6-- ax-5 1943. The forward implication can be seen as a strengthening of ax-5 1943 (a conjunct is added to the consequent of the implication). The reverse implication can be strengthened when ax-6 2000 is posited (which implies that models are non-empty), see 19.8v 2016. See bj-alextruim 37506 for a dual statement.

An approximate meaning is: the existential quantification of a proposition over a non-occurring variable holds if and only if the proposition holds and the universe is nonempty. (Contributed by BJ, 14-Mar-2026.) (Proof modification is discouraged.)

(∃𝑥𝜑 ↔ (∃𝑥⊤ ∧ 𝜑))
 
14-Mar-2026bj-alextruim 37506 An equivalent expression for universal quantification over a non-occurring variable proved over ax-1 6-- ax-5 1943. The forward implication can be strengthened when ax-6 2000 is posited (which implies that models are non-empty), see spvw 2014. The reverse implication can be seen as a strengthening of ax-5 1943 (since the antecedent of the implication is weakened). See bj-exextruan 37507 for a dual statement.

An approximate meaning is: the universal quantification of a proposition over a non-occurring variable holds if and only if the proposition holds in nonempty universes. (Contributed by BJ, 14-Mar-2026.) (Proof modification is discouraged.)

(∀𝑥𝜑 ↔ (∃𝑥⊤ → 𝜑))
 
14-Mar-2026bj-exexalal 37446 A lemma for changing bound variables. Only the forward implication is intuitionistic. (Contributed by BJ, 14-Mar-2026.)
((∃𝑥𝜑 → ∃𝑦𝜓) ↔ (∀𝑦 ¬ 𝜓 → ∀𝑥 ¬ 𝜑))
 
11-Mar-2026axprglem 5394 Lemma for axprg 5395. (Contributed by GG, 11-Mar-2026.)
(𝑥 = 𝐴 → ∃𝑧∀𝑤((𝑤 = 𝐴 ∨ 𝑤 = 𝐵) → 𝑤 ∈ 𝑧))
 
8-Mar-2026bj-axnul 37956 Over the base theory ax-1 6-- ax-5 1943, the axiom of separation implies the weak emptyset axiom.

By "weak emptyset axiom", we mean the axiom asserting existence of an empty set (which can be called "the" empty set when the axiom of extensionality ax-ext 2733 is posited) provided existence of a set (the True truth constant existentially quantified over a fresh variable, extru 2008). This is the conclusion of bj-axnul 37956.

Note that the weak emptyset axiom implies (∃𝑥⊤ → ∃𝑦⊤) without DV conditions hence also the same statement as the weak emptyset axiom without DV conditions on 𝑥, but only on 𝑦, 𝑧.

By "axiom of separation", we mean the universal closure of ax-sep 5249, simulated here by its instance with ⊥ substituted for 𝜑 (and with the variable used to assert existence in the weak emptyset axiom substituted for the containing set) as the hypothesis of bj-axnul 37956.

In particular, the axiom of existence extru 2008 and the axiom of separation together imply the emptyset axiom (and conversely, the emptyset axiom implies the axiom of existence).

Note: this theorem does not require a disjointness condition on 𝑦, 𝑧, although both axioms should be stated with all variables disjoint.

This proof only uses an instance of the axiom of separation with a bounded formula, so is valid in a constructive setting (see the CZF section in the "Intuitionistic Logic Explorer" iset.mm). (Contributed by BJ, 8-Mar-2026.) (Proof modification is discouraged.)

∀𝑥∃𝑦∀𝑧(𝑧 ∈ 𝑦 ↔ (𝑧 ∈ 𝑥 ∧ ⊥))    ⇒   (∃𝑥⊤ → ∃𝑦∀𝑧 ∈ 𝑦 ⊥)
 
8-Mar-2026bj-cbvexvv 37509 Existentially quantifying over a non-occurring variable is independent of that variable, over ax-1 6-- ax-5 1943 and the existence axiom extru 2008. See bj-cbvew 37511 for a strengthening. (Contributed by BJ, 8-Mar-2026.) (Proof modification is discouraged.)
(∃𝑥𝜑 → (∃𝑦𝜓 → ∃𝑥𝜓))
 
8-Mar-2026bj-cbvalvv 37508 Universally quantifying over a non-occurring variable is independent of that variable, over ax-1 6-- ax-5 1943 and the existence axiom extru 2008. See bj-cbvaw 37510 for a strengthening. (Contributed by BJ, 8-Mar-2026.) (Proof modification is discouraged.)
(∃𝑥𝜑 → (∀𝑥𝜓 → ∀𝑦𝜓))
 
8-Mar-2026bj-spvew 37505 Version of 19.8v 2016 and 19.9v 2017 proved from ax-1 6-- ax-5 1943. The antecedent can for instance be proved with the existence axiom extru 2008. (Contributed by BJ, 8-Mar-2026.) This could also be proved from bj-spvw 37504 using duality, but that proof would not be intuitionistic, contrary to the present one. (Proof modification is discouraged.)
(∃𝑥𝜑 → (𝜓 ↔ ∃𝑥𝜓))
 
8-Mar-2026bj-spvw 37504 Version of spvw 2014 and 19.3v 2015 proved from ax-1 6-- ax-5 1943. The antecedent can for instance be proved with the existence axiom extru 2008. (Contributed by BJ, 8-Mar-2026.) (Proof modification is discouraged.)
(∃𝑥𝜑 → (𝜓 ↔ ∀𝑥𝜓))
 
8-Mar-2026bj-axdd2ALT 37489 Alternate proof of bj-axdd2 37432 (this should replace bj-axdd2 37432 when bj-exalimi 37485 is moved to the main section). (Contributed by BJ, 8-Mar-2026.) (Proof modification is discouraged.) (New usage is discouraged.)
(∃𝑥𝜑 → (∀𝑥𝜓 → ∃𝑥𝜓))
 
6-Mar-2026opex 5432 An ordered pair of classes is a set. Exercise 7 of [TakeutiZaring] p. 16. (Contributed by NM, 18-Aug-1993.) (Revised by Mario Carneiro, 26-Apr-2015.) Avoid ax-nul 5260. (Revised by GG, 6-Mar-2026.)
⟨𝐴, 𝐵⟩ ∈ V
 
6-Mar-2026snexg 5398 A singleton built on a set is a set. Special case of snex 5397 which is intuitionistically valid. (Contributed by NM, 7-Aug-1994.) (Revised by Mario Carneiro, 19-May-2013.) Extract from snex 5397 and shorten proof. (Revised by BJ, 15-Jan-2025.) (Proof shortened by GG, 6-Mar-2026.)
(𝐴 ∈ 𝑉 → {𝐴} ∈ V)
 
6-Mar-2026snex 5397 A singleton is a set. Theorem 7.12 of [Quine] p. 51, proved using Extensionality, Separation and Pairing. See also snexALT 5345. (Contributed by NM, 7-Aug-1994.) (Revised by Mario Carneiro, 19-May-2013.) Avoid ax-nul 5260 and shorten proof. (Revised by GG, 6-Mar-2026.)
{𝐴} ∈ V
 
6-Mar-2026prex 5396 The Axiom of Pairing using class variables. Theorem 7.13 of [Quine] p. 51. By virtue of its definition, an unordered pair remains a set (even though no longer a pair) even when its components are proper classes (see prprc 4728), so we can dispense with hypotheses requiring them to be sets. (Contributed by NM, 15-Jul-1993.) Avoid ax-nul 5260 and shorten proof. (Revised by GG, 6-Mar-2026.)
{𝐴, 𝐵} ∈ V
 
6-Mar-2026axprg 5395 Derive The Axiom of Pairing with class variables. (Contributed by GG, 6-Mar-2026.)
∃𝑧∀𝑤((𝑤 = 𝐴 ∨ 𝑤 = 𝐵) → 𝑤 ∈ 𝑧)
 
5-Mar-2026mh-setindnd 37295 A version of mh-setind 37294 with no distinct variable conditions. (Contributed by Matthew House, 5-Mar-2026.) (New usage is discouraged.)
(∀𝑦(∀𝑥(𝑥 ∈ 𝑦 → 𝜑) → ∀𝑥(𝑥 = 𝑦 → ∀𝑦𝜑)) → 𝜑)
 
4-Mar-2026regsfromunir1 37298 Derivation of ax-regs 35767 from unir1 9803. (Contributed by Matthew House, 4-Mar-2026.)
∪ (𝑅1 “ On) = V    ⇒   (∃𝑥𝜑 → ∃𝑦(∀𝑥(𝑥 = 𝑦 → 𝜑) ∧ ∀𝑧(𝑧 ∈ 𝑦 → ¬ ∀𝑥(𝑥 = 𝑧 → 𝜑))))
 
4-Mar-2026regsfromsetind 37297 Derivation of ax-regs 35767 from mh-setind 37294. (Contributed by Matthew House, 4-Mar-2026.)
(∀𝑦(∀𝑥(𝑥 ∈ 𝑦 → ¬ 𝜑) → ∀𝑥(𝑥 = 𝑦 → ¬ 𝜑)) → ¬ 𝜑)    ⇒   (∃𝑥𝜑 → ∃𝑦(∀𝑥(𝑥 = 𝑦 → 𝜑) ∧ ∀𝑧(𝑧 ∈ 𝑦 → ¬ ∀𝑥(𝑥 = 𝑧 → 𝜑))))
 
4-Mar-2026regsfromregtco 37296 Derivation of ax-regs 35767 from ax-reg 9570 + ax-tco 37230. (Contributed by Matthew House, 4-Mar-2026.)
(∃𝑦 𝑦 ∈ 𝑤 → ∃𝑦(𝑦 ∈ 𝑤 ∧ ∀𝑧(𝑧 ∈ 𝑦 → ¬ 𝑧 ∈ 𝑤)))    &   ∃𝑢(𝑣 ∈ 𝑢 ∧ ∀𝑡(𝑡 ∈ 𝑢 → ∀𝑠(𝑠 ∈ 𝑡 → 𝑠 ∈ 𝑢)))    ⇒   (∃𝑥𝜑 → ∃𝑦(∀𝑥(𝑥 = 𝑦 → 𝜑) ∧ ∀𝑧(𝑧 ∈ 𝑦 → ¬ ∀𝑥(𝑥 = 𝑧 → 𝜑))))
 
4-Mar-2026mh-setind 37294 Principle of set induction setind 9732, written with primitive symbols. (Contributed by Matthew House, 4-Mar-2026.)
(∀𝑦(∀𝑥(𝑥 ∈ 𝑦 → 𝜑) → ∀𝑥(𝑥 = 𝑦 → 𝜑)) → 𝜑)
 
27-Feb-2026eln0s2 28725 A non-negative surreal integer is a surreal ordinal with a finite birthday. (Contributed by Scott Fenton, 27-Feb-2026.)
(𝐴 ∈ ℕ0s ↔ (𝐴 ∈ Ons ∧ ( bday ‘𝐴) ∈ ω))
 
27-Feb-2026peano2n0sd 28699 Peano postulate: the successor of a non-negative surreal integer is a non-negative surreal integer. Deduction form. (Contributed by Scott Fenton, 27-Feb-2026.)
(𝜑 → 𝐴 ∈ ℕ0s)    ⇒   (𝜑 → (𝐴 +s 1s ) ∈ ℕ0s)
 
27-Feb-2026divs1d 28573 A surreal divided by one is itself. Deduction version. (Contributed by Scott Fenton, 27-Feb-2026.)
(𝜑 → 𝐴 ∈ No )    ⇒   (𝜑 → (𝐴 /su 1s ) = 𝐴)
 
27-Feb-2026rightnod 28250 An element of a right set is a surreal. (Contributed by Scott Fenton, 27-Feb-2026.)
(𝜑 → 𝐴 ∈ ( R ‘𝐵))    ⇒   (𝜑 → 𝐴 ∈ No )
 
27-Feb-2026rightoldd 28249 An element of a right set is an element of the old set. (Contributed by Scott Fenton, 27-Feb-2026.)
(𝜑 → 𝐴 ∈ ( R ‘𝐵))    ⇒   (𝜑 → 𝐴 ∈ ( O ‘( bday ‘𝐵)))
 
27-Feb-2026leftnod 28248 An element of a left set is a surreal. (Contributed by Scott Fenton, 27-Feb-2026.)
(𝜑 → 𝐴 ∈ ( L ‘𝐵))    ⇒   (𝜑 → 𝐴 ∈ No )
 
27-Feb-2026leftoldd 28247 An element of a left set is an element of the old set. (Contributed by Scott Fenton, 27-Feb-2026.)
(𝜑 → 𝐴 ∈ ( L ‘𝐵))    ⇒   (𝜑 → 𝐴 ∈ ( O ‘( bday ‘𝐵)))
 
27-Feb-2026rightno 28246 An element of a right set is a surreal. (Contributed by Scott Fenton, 27-Feb-2026.)
(𝐴 ∈ ( R ‘𝐵) → 𝐴 ∈ No )
 
27-Feb-2026leftno 28245 An element of a left set is a surreal. (Contributed by Scott Fenton, 27-Feb-2026.)
(𝐴 ∈ ( L ‘𝐵) → 𝐴 ∈ No )
 
27-Feb-2026rightold 28244 An element of a right set is an element of the old set. (Contributed by Scott Fenton, 27-Feb-2026.)
(𝐴 ∈ ( R ‘𝐵) → 𝐴 ∈ ( O ‘( bday ‘𝐵)))
 
27-Feb-2026leftold 28243 An element of a left set is an element of the old set. (Contributed by Scott Fenton, 27-Feb-2026.)
(𝐴 ∈ ( L ‘𝐵) → 𝐴 ∈ ( O ‘( bday ‘𝐵)))
 
27-Feb-2026oldmaded 28237 An element of an old set is an element of a made set. (Contributed by Scott Fenton, 27-Feb-2026.)
(𝜑 → 𝐴 ∈ ( O ‘𝐵))    ⇒   (𝜑 → 𝐴 ∈ ( M ‘𝐵))
 
27-Feb-2026oldmade 28236 An element of an old set is an element of a made set. (Contributed by Scott Fenton, 27-Feb-2026.)
(𝐴 ∈ ( O ‘𝐵) → 𝐴 ∈ ( M ‘𝐵))
 
27-Feb-2026newnod 28216 An element of a new set is a surreal. (Contributed by Scott Fenton, 27-Feb-2026.)
(𝜑 → 𝐴 ∈ ( N ‘𝐵))    ⇒   (𝜑 → 𝐴 ∈ No )

Older news:

(29-Jul-2020) Mario Carneiro presented MM0 at the CICM conference. See this Google Group post which includes a YouTube link.

(20-Jul-2020) Rohan Ridenour found 5 shorter D-proofs in our Shortest known proofs... file. In particular, he reduced *4.39 from 901 to 609 steps. A note on the Metamath Solitaire page mentions a tool that he worked with.

(19-Jul-2020) David A. Wheeler posted a video (https://youtu.be/3R27Qx69jHc) on how to (re)prove Schwabh�user 4.6 for the Metamath Proof Explorer. See also his older videos.

(19-Jul-2020) In version 0.184 of the metamath program, "verify markup" now checks that mathboxes are independent i.e. do not cross-reference each other. To turn off this check, use "/mathbox_skip"

(30-Jun-2020) In version 0.183 of the metamath program, (1) "verify markup" now has checking for (i) underscores in labels, (ii) that *ALT and *OLD theorems have both discouragement tags, and (iii) that lines don't have trailing spaces. (2) "save proof.../rewrap" no longer left-aligns $p/$a comments that contain the string "<HTML>"; see this note.

(5-Apr-2020) Glauco Siliprandi added a new proof to the 100 theorem list, e is Transcendental etransc, bringing the Metamath total to 74.

(12-Feb-2020) A bug in the 'minimize' command of metamath.exe versions 0.179 (29-Nov-2019) and 0.180 (10-Dec-2019) may incorrectly bring in the use of new axioms. Version 0.181 fixes it.

(20-Jan-2020) David A. Wheeler created a video called Walkthrough of the tutorial in mmj2. See the Google Group announcement for more details. (All of his videos are listed on the Other Metamath-Related Topics page.)

(18-Jan-2020) The FOMM 2020 talks are on youtube now. Mario Carneiro's talk is Metamath Zero, or: How to Verify a Verifier. Since they are washed out in the video, the PDF slides are available separately.

(14-Dec-2019) Glauco Siliprandi added a new proof to the 100 theorem list, Fourier series convergence fourier, bringing the Metamath total to 73.

(25-Nov-2019) Alexander van der Vekens added a new proof to the 100 theorem list, The Cayley-Hamilton Theorem cayleyhamilton, bringing the Metamath total to 72.

(25-Oct-2019) Mario Carneiro's paper "Metamath Zero: The Cartesian Theorem Prover" (submitted to CPP 2020) is now available on arXiv: https://arxiv.org/abs/1910.10703. There is a related discussion on Hacker News.

(30-Sep-2019) Mario Carneiro's talk about MM0 at ITP 2019 is available on YouTube: x86 verification from scratch (24 minutes). Google Group discussion: Metamath Zero.

(29-Sep-2019) David Wheeler created a fascinating Gource video that animates the construction of set.mm, available on YouTube: Metamath set.mm contributions viewed with Gource through 2019-09-26 (4 minutes). Google Group discussion: Gource video of set.mm contributions.

(24-Sep-2019) nLab added a page for Metamath. It mentions Stefan O'Rear's Busy Beaver work using the set.mm axiomatization (and fails to mention Mario's definitional soundness checker)

(1-Sep-2019) Xuanji Li published a Visual Studio Code extension to support metamath syntax highlighting.

(10-Aug-2019) (revised 21-Sep-2019) Version 0.178 of the metamath program has the following changes: (1) "minimize_with" will now prevent dependence on new $a statements unless the new qualifier "/allow_new_axioms" is specified. For routine usage, it is suggested that you use "minimize_with * /allow_new_axioms * /no_new_axioms_from ax-*" instead of just "minimize_with *". See "help minimize_with" and this Google Group post. Also note that the qualifier "/allow_growth" has been renamed to "/may_grow". (2) "/no_versioning" was added to "write theorem_list".

(8-Jul-2019) Jon Pennant announced the creation of a Metamath search engine. Try it and feel free to comment on it at https://groups.google.com/d/msg/metamath/cTeU5AzUksI/5GesBfDaCwAJ.

(16-May-2019) Set.mm now has a major new section on elementary geometry. This begins with definitions that implement Tarski's axioms of geometry (including concepts such as congruence and betweenness). This uses set.mm's extensible structures, making them easier to use for many circumstances. The section then connects Tarski geometry with geometry in Euclidean places. Most of the work in this section is due to Thierry Arnoux, with earlier work by Mario Carneiro and Scott Fenton. [Reported by DAW.]

(9-May-2019) We are sad to report that long-time contributor Alan Sare passed away on Mar. 23. There is some more information at the top of his mathbox (click on "Mathbox for Alan Sare") and his obituary. We extend our condolences to his family.

(10-Mar-2019) Jon Pennant and Mario Carneiro added a new proof to the 100 theorem list, Heron's formula heron, bringing the Metamath total to 71.

(22-Feb-2019) Alexander van der Vekens added a new proof to the 100 theorem list, Cramer's rule cramer, bringing the Metamath total to 70.

(6-Feb-2019) David A. Wheeler has made significant improvements and updates to the Metamath book. Any comments, errors found, or suggestions are welcome and should be turned into an issue or pull request at https://github.com/metamath/metamath-book (or sent to me if you prefer).

(26-Dec-2018) I added Appendix 8 to the MPE Home Page that cross-references new and old axiom numbers.

(20-Dec-2018) The axioms have been renumbered according to this Google Groups post.

(24-Nov-2018) Thierry Arnoux created a new page on topological structures. The page along with its SVG files are maintained on GitHub.

(11-Oct-2018) Alexander van der Vekens added a new proof to the 100 theorem list, the Friendship Theorem friendship, bringing the Metamath total to 69.

(1-Oct-2018) Naip Moro has written gramm, a Metamath proof verifier written in Antlr4/Java.

(16-Sep-2018) The definition df-riota has been simplified so that it evaluates to the empty set instead of an Undef value. This change affects a significant part of set.mm.

(2-Sep-2018) Thierry Arnoux added a new proof to the 100 theorem list, Euler's partition theorem eulerpart, bringing the Metamath total to 68.

(1-Sep-2018) The Kate editor now has Metamath syntax highlighting built in. (Communicated by Wolf Lammen.)

(15-Aug-2018) The Intuitionistic Logic Explorer now has a Most Recent Proofs page.

(4-Aug-2018) Version 0.163 of the metamath program now indicates (with an asterisk) which Table of Contents headers have associated comments.

(10-May-2018) George Szpiro, journalist and author of several books on popular mathematics such as Poincare's Prize and Numbers Rule, used a genetic algorithm to find shorter D-proofs of "*3.37" and "meredith" in our Shortest known proofs... file.

(19-Apr-2018) The EMetamath Eclipse plugin has undergone many improvements since its initial release as the change log indicates. Thierry uses it as his main proof assistant and writes, "I added support for mmj2's auto-transformations, which allows it to infer several steps when building proofs. This added a lot of comfort for writing proofs.... I can now switch back and forth between the proof assistant and editing the Metamath file.... I think no other proof assistant has this feature."

(11-Apr-2018) Benoît Jubin solved an open problem about the "Axiom of Twoness," showing that it is necessary for completeness. See item 14 on the "Open problems and miscellany" page.

(25-Mar-2018) Giovanni Mascellani has announced mmpp, a new proof editing environment for the Metamath language.

(27-Feb-2018) Bill Hale has released an app for the Apple iPad and desktop computer that allows you to browse Metamath theorems and their proofs.

(17-Jan-2018) Dylan Houlihan has kindly provided a new mirror site. He has also provided an rsync server; type "rsync uk.metamath.org::" in a bash shell to check its status (it should return "metamath metamath").

(15-Jan-2018) The metamath program, version 0.157, has been updated to implement the file inclusion conventions described in the 21-Dec-2017 entry of mmnotes.txt.

(11-Dec-2017) I added a paragraph, suggested by Gérard Lang, to the distinct variable description here.

(10-Dec-2017) Per FL's request, his mathbox will be removed from set.mm. If you wish to export any of his theorems, today's version (master commit 1024a3a) is the last one that will contain it.

(11-Nov-2017) Alan Sare updated his completeusersproof program.

(3-Oct-2017) Sean B. Palmer created a web page that runs the metamath program under emulated Linux in JavaScript. He also wrote some programs to work with our shortest known proofs of the PM propositional calculus theorems.

(28-Sep-2017) Ivan Kuckir wrote a tutorial blog entry, Introduction to Metamath, that summarizes the language syntax. (It may have been written some time ago, but I was not aware of it before.)

(26-Sep-2017) The default directory for the Metamath Proof Explorer (MPE) has been changed from the GIF version (mpegif) to the Unicode version (mpeuni) throughout the site. Please let me know if you find broken links or other issues.

(24-Sep-2017) Saveliy Skresanov added a new proof to the 100 theorem list, Ceva's Theorem cevath, bringing the Metamath total to 67.

(3-Sep-2017) Brendan Leahy added a new proof to the 100 theorem list, Area of a Circle areacirc, bringing the Metamath total to 66.

(7-Aug-2017) Mario Carneiro added a new proof to the 100 theorem list, Principle of Inclusion/Exclusion incexc, bringing the Metamath total to 65.

(1-Jul-2017) Glauco Siliprandi added a new proof to the 100 theorem list, Stirling's Formula stirling, bringing the Metamath total to 64. Related theorems include 2 versions of Wallis' formula for π (wallispi and wallispi2).

(7-May-2017) Thierry Arnoux added a new proof to the 100 theorem list, Betrand's Ballot Problem ballotth, bringing the Metamath total to 63.

(20-Apr-2017) Glauco Siliprandi added a new proof in the supplementary list on the 100 theorem list, Stone-Weierstrass Theorem stowei.

(28-Feb-2017) David Moews added a new proof to the 100 theorem list, Product of Segments of Chords chordthm, bringing the Metamath total to 62.

(1-Jan-2017) Saveliy Skresanov added a new proof to the 100 theorem list, Isosceles triangle theorem isosctr, bringing the Metamath total to 61.

(1-Jan-2017) Mario Carneiro added 2 new proofs to the 100 theorem list, L'Hôpital's Rule lhop and Taylor's Theorem taylth, bringing the Metamath total to 60.

(28-Dec-2016) David A. Wheeler is putting together a page on Metamath (specifically set.mm) conventions. Comments are welcome on the Google Group thread.

(24-Dec-2016) Mario Carneiro introduced the abbreviation "F/ x ph" (symbols: turned F, x, phi) in df-nf to represent the "effectively not free" idiom "A. x ( ph -> A. x ph )". Theorem nf2 shows a version without nested quantifiers.

(22-Dec-2016) Naip Moro has developed a Metamath database for G. Spencer-Brown's Laws of Form. You can follow the Google Group discussion here.

(20-Dec-2016) In metamath program version 0.137, 'verify markup *' now checks that ax-XXX $a matches axXXX $p when the latter exists, per the discussion at https://groups.google.com/d/msg/metamath/Vtz3CKGmXnI/Fxq3j1I_EQAJ.

(24-Nov-2016) Mingl Yuan has kindly provided a mirror site in Beijing, China. He has also provided an rsync server; type "rsync cn.metamath.org::" in a bash shell to check its status (it should return "metamath metamath").

(14-Aug-2016) All HTML pages on this site should now be mobile-friendly and pass the Mobile-Friendly Test. If you find one that does not, let me know.

(14-Aug-2016) Daniel Whalen wrote a paper describing the use of using deep learning to prove 14% of test theorems taken from set.mm: Holophrasm: a neural Automated Theorem Prover for higher-order logic. The associated program is called Holophrasm.

(14-Aug-2016) David A. Wheeler created a video called Metamath Proof Explorer: A Modern Principia Mathematica

(12-Aug-2016) A Gitter chat room has been created for Metamath.

(9-Aug-2016) Mario Carneiro wrote a Metamath proof verifier in the Scala language as part of the ongoing Metamath -> MMT import project

(9-Aug-2016) David A. Wheeler created a GitHub project called metamath-test (last execution run) to check that different verifiers both pass good databases and detect errors in defective ones.

(4-Aug-2016) Mario gave two presentations at CICM 2016.

(17-Jul-2016) Thierry Arnoux has written EMetamath, a Metamath plugin for the Eclipse IDE.

(16-Jul-2016) Mario recovered Chris Capel's collapsible proof demo.

(13-Jul-2016) FL sent me an updated version of PDF (LaTeX source) developed with Lamport's pf2 package. See the 23-Apr-2012 entry below.

(12-Jul-2016) David A. Wheeler produced a new video for mmj2 called "Creating functions in Metamath". It shows a more efficient approach than his previous recent video "Creating functions in Metamath" (old) but it can be of interest to see both approaches.

(10-Jul-2016) Metamath program version 0.132 changes the command 'show restricted' to 'show discouraged' and adds a new command, 'set discouragement'. See the mmnotes.txt entry of 11-May-2016 (updated 10-Jul-2016).

(12-Jun-2016) Dan Getz has written Metamath.jl, a Metamath proof verifier written in the Julia language.

(10-Jun-2016) If you are using metamath program versions 0.128, 0.129, or 0.130, please update to version 0.131. (In the bad versions, 'minimize_with' ignores distinct variable violations.)

(1-Jun-2016) Mario Carneiro added new proofs to the 100 theorem list, the Prime Number Theorem pnt and the Perfect Number Theorem perfect, bringing the Metamath total to 58.

(12-May-2016) Mario Carneiro added a new proof to the 100 theorem list, Dirichlet's theorem dirith, bringing the Metamath total to 56. (Added 17-May-2016) An informal exposition of the proof can be found at http://metamath-blog.blogspot.com/2016/05/dirichlets-theorem.html

(10-Mar-2016) Metamath program version 0.125 adds a new qualifier, /fast, to 'save proof'. See the mmnotes.txt entry of 10-Mar-2016.

(6-Mar-2016) The most recent set.mm has a large update converting variables from letters to symbols. See this Google Groups post.

(16-Feb-2016) Mario Carneiro's new paper "Models for Metamath" can be found here and on arxiv.org.

(6-Feb-2016) There are now 22 math symbols that can be used as variable names. See mmascii.html near the 50th table row, starting with "./\".

(29-Jan-2016) Metamath program version 0.123 adds /packed and /explicit qualifiers to 'save proof' and 'show proof'. See this Google Groups post.

(13-Jan-2016) The Unicode math symbols now provide for external CSS and use the XITS web font. Thanks to David A. Wheeler, Mario Carneiro, Cris Perdue, Jason Orendorff, and Frédéric Liné for discussions on this topic. Two commands, htmlcss and htmlfont, were added to the $t comment in set.mm and are recognized by Metamath program version 0.122.

(21-Dec-2015) Axiom ax-12, now renamed ax-12o, was replaced by a new shorter equivalent, ax-12. The equivalence is provided by theorems ax12o and ax12.

(13-Dec-2015) A new section on the theory of classes was added to the MPE Home Page. Thanks to Gérard Lang for suggesting this section and improvements to it.

(17-Nov-2015) Metamath program version 0.121: 'verify markup' was added to check comment markup consistency; see 'help verify markup'. You are encouraged to make sure 'verify markup */f' has no warnings prior to mathbox submissions. The date consistency rules are given in this Google Groups post.

(23-Sep-2015) Drahflow wrote, "I am currently working on yet another proof assistant, main reason being: I understand stuff best if I code it. If anyone is interested: https://github.com/Drahflow/Igor (but in my own programming language, so expect a complicated build process :P)"

(23-Aug-2015) Ivan Kuckir created MM Tool, a Metamath proof verifier and editor written in JavaScript that runs in a browser.

(25-Jul-2015) Axiom ax-10 is shown to be redundant by theorem ax10 , so it was removed from the predicate calculus axiom list.

(19-Jul-2015) Mario Carneiro gave two talks related to Metamath at CICM 2015, which are linked to at Other Metamath-Related Topics.

(18-Jul-2015) The metamath program has been updated to version 0.118. 'show trace_back' now has a '/to' qualifier to show the path back to a specific axiom such as ax-ac. See 'help show trace_back'.

(12-Jul-2015) I added the HOL Explorer for Mario Carneiro's hol.mm database. Although the home page needs to be filled out, the proofs can be accessed.

(11-Jul-2015) I started a new page, Other Metamath-Related Topics, that will hold miscellaneous material that doesn't fit well elsewhere (or is hard to find on this site). Suggestions welcome.

(23-Jun-2015) Metamath's mascot, Penny the cat (2007 photo), passed away today. She was 18 years old.

(21-Jun-2015) Mario Carneiro added 3 new proofs to the 100 theorem list: All Primes (1 mod 4) Equal the Sum of Two Squares 2sq, The Law of Quadratic Reciprocity lgsquad and the AM-GM theorem amgm, bringing the Metamath total to 55.

(13-Jun-2015) Stefan O'Rear's smm, written in JavaScript, can now be used as a standalone proof verifier. This brings the total number of independent Metamath verifiers to 8, written in just as many languages (C, Java. JavaScript, Python, Haskell, Lua, C#, C++).

(12-Jun-2015) David A. Wheeler added 2 new proofs to the 100 theorem list: The Law of Cosines lawcos and Ptolemy's Theorem ptolemy, bringing the Metamath total to 52.

(30-May-2015) The metamath program has been updated to version 0.117. (1) David A. Wheeler provided an enhancement to speed up the 'improve' command by 28%; see README.TXT for more information. (2) In web pages with proofs, local hyperlinks on step hypotheses no longer clip the Expression cell at the top of the page.

(9-May-2015) Stefan O'Rear has created an archive of older set.mm releases back to 1998: https://github.com/sorear/set.mm-history/.

(7-May-2015) The set.mm dated 7-May-2015 is a major revision, updated by Mario, that incorporates the new ordered pair definition df-op that was agreed upon. There were 700 changes, listed at the top of set.mm. Mathbox users are advised to update their local mathboxes. As usual, if any mathbox user has trouble incorporating these changes into their mathbox in progress, Mario or I will be glad to do them for you.

(7-May-2015) Mario has added 4 new theorems to the 100 theorem list: Ramsey's Theorem ramsey, The Solution of a Cubic cubic, The Solution of the General Quartic Equation quart, and The Birthday Problem birthday. In the Supplementary List, Stefan O'Rear added the Hilbert Basis Theorem hbt.

(28-Apr-2015) A while ago, Mario Carneiro wrote up a proof of the unambiguity of set.mm's grammar, which has now been added to this site: grammar-ambiguity.txt.

(22-Apr-2015) The metamath program has been updated to version 0.114. In MM-PA, 'show new_proof/unknown' now shows the relative offset (-1, -2,...) used for 'assign' arguments, suggested by Stefan O'Rear.

(20-Apr-2015) I retrieved an old version of the missing "Metamath 100" page from archive.org and updated it to what I think is the current state: mm_100.html. Anyone who wants to edit it can email updates to this page to me.

(19-Apr-2015) The metamath program has been updated to version 0.113, mostly with patches provided by Stefan O'Rear. (1) 'show statement %' (or any command allowing label wildcards) will select statements whose proofs were changed in current session. ('help search' will show all wildcard matching rules.) (2) 'show statement =' will select the statement being proved in MM-PA. (3) The proof date stamp is now created only if the proof is complete.

(18-Apr-2015) There is now a section for Scott Fenton's NF database: New Foundations Explorer.

(16-Apr-2015) Mario describes his recent additions to set.mm at https://groups.google.com/forum/#!topic/metamath/VAGNmzFkHCs. It include 2 new additions to the Formalizing 100 Theorems list, Leibniz' series for pi (leibpi) and the Konigsberg Bridge problem (konigsberg)

(10-Mar-2015) Mario Carneiro has written a paper, "Arithmetic in Metamath, Case Study: Bertrand's Postulate," for CICM 2015. A preprint is available at arXiv:1503.02349.

(23-Feb-2015) Scott Fenton has created a Metamath formalization of NF set theory: https://github.com/sctfn/metamath-nf/. For more information, see the Metamath Google Group posting.

(28-Jan-2015) Mario Carneiro added Wilson's Theorem (wilth), Ascending or Descending Sequences (erdsze, erdsze2), and Derangements Formula (derangfmla, subfaclim), bringing the Metamath total for Formalizing 100 Theorems to 44.

(19-Jan-2015) Mario Carneiro added Sylow's Theorem (sylow1, sylow2, sylow2b, sylow3), bringing the Metamath total for Formalizing 100 Theorems to 41.

(9-Jan-2015) The hypothesis order of mpbi*an* was changed. See the Notes entry of 9-Jan-2015.

(1-Jan-2015) Mario Carneiro has written a paper, "Conversion of HOL Light proofs into Metamath," that has been submitted to the Journal of Formalized Reasoning. A preprint is available on arxiv.org.

(22-Nov-2014) Stefan O'Rear added the Solutions to Pell's Equation (rmxycomplete) and Liouville's Theorem and the Construction of Transcendental Numbers (aaliou), bringing the Metamath total for Formalizing 100 Theorems to 40.

(22-Nov-2014) The metamath program has been updated with version 0.111. (1) Label wildcards now have a label range indicator "~" so that e.g. you can show or search all of the statements in a mathbox. See 'help search'. (Stefan O'Rear added this to the program.) (2) A qualifier was added to 'minimize_with' to prevent the use of any axioms not already used in the proof e.g. 'minimize_with * /no_new_axioms_from ax-*' will prevent the use of ax-ac if the proof doesn't already use it. See 'help minimize_with'.

(10-Oct-2014) Mario Carneiro has encoded the axiomatic basis for the HOL theorem prover into a Metamath source file, hol.mm.

(24-Sep-2014) Mario Carneiro added the Sum of the Angles of a Triangle (ang180), bringing the Metamath total for Formalizing 100 Theorems to 38.

(15-Sep-2014) Mario Carneiro added the Fundamental Theorem of Algebra (fta), bringing the Metamath total for Formalizing 100 Theorems to 37.

(3-Sep-2014) Mario Carneiro added the Fundamental Theorem of Integral Calculus (ftc1, ftc2). This brings the Metamath total for Formalizing 100 Theorems to 35. (added 14-Sep-2014) Along the way, he added the Mean Value Theorem (mvth), bringing the total to 36.

(16-Aug-2014) Mario Carneiro started a Metamath blog at http://metamath-blog.blogspot.com/.

(10-Aug-2014) Mario Carneiro added Erdős's proof of the divergence of the inverse prime series (prmrec). This brings the Metamath total for Formalizing 100 Theorems to 34.

(31-Jul-2014) Mario Carneiro added proofs for Euler's Summation of 1 + (1/2)^2 + (1/3)^2 + .... (basel) and The Factor and Remainder Theorems (facth, plyrem). This brings the Metamath total for Formalizing 100 Theorems to 33.

(16-Jul-2014) Mario Carneiro added proofs for Four Squares Theorem (4sq), Formula for the Number of Combinations (hashbc), and Divisibility by 3 Rule (3dvds). This brings the Metamath total for Formalizing 100 Theorems to 31.

(11-Jul-2014) Mario Carneiro added proofs for Divergence of the Harmonic Series (harmonic), Order of a Subgroup (lagsubg), and Lebesgue Measure and Integration (itgcl). This brings the Metamath total for Formalizing 100 Theorems to 28.

(7-Jul-2014) Mario Carneiro presented a talk, "Natural Deduction in the Metamath Proof Language," at the 6PCM conference. Slides Audio

(25-Jun-2014) In version 0.108 of the metamath program, the 'minimize_with' command is now more automated. It now considers compressed proof length; it scans the statements in forward and reverse order and chooses the best; and it avoids $d conflicts. The '/no_distinct', '/brief', and '/reverse' qualifiers are obsolete, and '/verbose' no longer lists all statements scanned but gives more details about decision criteria.

(12-Jun-2014) To improve naming uniformity, theorems about operation values now use the abbreviation "ov". For example, df-opr, opreq1, oprabval5, and oprvres are now called df-ov, oveq1, ov5, and ovres respectively.

(11-Jun-2014) Mario Carneiro finished a major revision of set.mm. His notes are under the 11-Jun-2014 entry in the Notes

(4-Jun-2014) Mario Carneiro provided instructions and screenshots for syntax highlighting for the jEdit editor for use with Metamath and mmj2 source files.

(19-May-2014) Mario Carneiro added a feature to mmj2, in the build at https://github.com/digama0/mmj2/raw/dev-build/mmj2jar/mmj2.jar, which tests all but 5 definitions in set.mm for soundness. You can turn on the test by adding
SetMMDefinitionsCheckWithExclusions,ax-*,df-bi,df-clab,df-cleq,df-clel,df-sbc
to your RunParms.txt file.

(17-May-2014) A number of labels were changed in set.mm, listed at the top of set.mm as usual. Note in particular that the heavily-used visset, elisseti, syl11anc, syl111anc were changed respectively to vex, elexi, syl2anc, syl3anc.

(16-May-2014) Scott Fenton formalized a proof for "Sum of kth powers": fsumkthpow. This brings the Metamath total for Formalizing 100 Theorems to 25.

(9-May-2014) I (Norm Megill) presented an overview of Metamath at the "Formalization of mathematics in proof assistants" workshop at the Institut Henri Poincar� in Paris. The slides for this talk are here.

(22-Jun-2014) Version 0.107 of the metamath program adds a "PART" indention level to the Statement List table of contents, adds 'show proof ... /size' to show source file bytes used, and adds 'show elapsed_time'. The last one is helpful for measuring the run time of long commands. See 'help write theorem_list', 'help show proof', and 'help show elapsed_time' for more information.

(2-May-2014) Scott Fenton formalized a proof of Sum of the Reciprocals of the Triangular Numbers: trirecip. This brings the Metamath total for Formalizing 100 Theorems to 24.

(19-Apr-2014) Scott Fenton formalized a proof of the Formula for Pythagorean Triples: pythagtrip. This brings the Metamath total for Formalizing 100 Theorems to 23.

(11-Apr-2014) David A. Wheeler produced a much-needed and well-done video for mmj2, called "Introduction to Metamath & mmj2". Thanks, David!

(15-Mar-2014) Mario Carneiro formalized a proof of Bertrand's postulate: bpos. This brings the Metamath total for Formalizing 100 Theorems to 22.

(18-Feb-2014) Mario Carneiro proved that complex number axiom ax-cnex is redundant (theorem cnex). See also Real and Complex Numbers.

(11-Feb-2014) David A. Wheeler has created a theorem compilation that tracks those theorems in Freek Wiedijk's Formalizing 100 Theorems list that have been proved in set.mm. If you find a error or omission in this list, let me know so it can be corrected. (Update 1-Mar-2014: Mario has added eulerth and bezout to the list.)

(4-Feb-2014) Mario Carneiro writes:

The latest commit on the mmj2 development branch introduced an exciting new feature, namely syntax highlighting for mmp files in the main window. (You can pick up the latest mmj2.jar at https://github.com/digama0/mmj2/blob/develop/mmj2jar/mmj2.jar .) The reason I am asking for your help at this stage is to help with design for the syntax tokenizer, which is responsible for breaking down the input into various tokens with names like "comment", "set", and "stephypref", which are then colored according to the user's preference. As users of mmj2 and metamath, what types of highlighting would be useful to you?

One limitation of the tokenizer is that since (for performance reasons) it can be started at any line in the file, highly contextual coloring, like highlighting step references that don't exist previously in the file, is difficult to do. Similarly, true parsing of the formulas using the grammar is possible but likely to be unmanageably slow. But things like checking theorem labels against the database is quite simple to do under the current setup.

That said, how can this new feature be optimized to help you when writing proofs?

(13-Jan-2014) Mathbox users: the *19.21a*, *19.23a* series of theorems have been renamed to *alrim*, *exlim*. You can update your mathbox with a global replacement of string '19.21a' with 'alrim' and '19.23a' with 'exlim'.

(5-Jan-2014) If you downloaded mmj2 in the past 3 days, please update it with the current version, which fixes a bug introduced by the recent changes that made it unable to read in most of the proofs in the textarea properly.

(4-Jan-2014) I added a list of "Allowed substitutions" under the "Distinct variable groups" list on the theorem web pages, for example axsep. This is an experimental feature and comments are welcome.

(3-Jan-2014) Version 0.102 of the metamath program produces more space-efficient compressed proofs (still compatible with the specification in Appendix B of the Metamath book) using an algorithm suggested by Mario Carneiro. See 'help save proof' in the program. Also, mmj2 now generates proofs in the new format. The new mmj2 also has a mandatory update that fixes a bug related to the new format; you must update your mmj2 copy to use it with the latest set.mm.

(23-Dec-2013) Mario Carneiro has updated many older definitions to use the maps-to notation. If you have difficulty updating your local mathbox, contact him or me for assistance.

(1-Nov-2013) 'undo' and 'redo' commands were added to the Proof Assistant in metamath program version 0.07.99. See 'help undo' in the program.

(8-Oct-2013) Today's Notes entry describes some proof repair techniques.

(5-Oct-2013) Today's Notes entry explains some recent extensible structure improvements.

(8-Sep-2013) Mario Carneiro has revised the square root and sequence generator definitions. See today's Notes entry.

(3-Aug-2013) Mario Carneiro writes: "I finally found enough time to create a GitHub repository for development at https://github.com/digama0/mmj2. A permalink to the latest version plus source (akin to mmj2.zip) is https://github.com/digama0/mmj2/zipball/, and the jar file on its own (mmj2.jar) is at https://github.com/digama0/mmj2/blob/master/mmj2jar/mmj2.jar?raw=true. Unfortunately there is no easy way to automatically generate mmj2jar.zip, but this is available as part of the zip distribution for mmj2.zip. History tracking will be handled by the repository now. Do you have old versions of the mmj2 directory? I could add them as historical commits if you do."

(18-Jun-2013) Mario Carneiro has done a major revision and cleanup of the construction of real and complex numbers. In particular, rather than using equivalence classes as is customary for the construction of the temporary rationals, he used only "reduced fractions", so that the use of the axiom of infinity is avoided until it becomes necessary for the construction of the temporary reals.

(18-May-2013) Mario Carneiro has added the ability to produce compressed proofs to mmj2. This is not an official release but can be downloaded here if you want to try it: mmj2.jar. If you have any feedback, send it to me (NM), and I will forward it to Mario. (Disclaimer: this release has not been endorsed by Mel O'Cat. If anyone has been in contact with him, please let me know.)

(29-Mar-2013) Charles Greathouse reduced the size of our PNG symbol images using the pngout program.

(8-Mar-2013) Wolf Lammen has reorganized the theorems in the "Logical negation" section of set.mm into a more orderly, less scattered arrangement.

(27-Feb-2013) Scott Fenton has done a large cleanup of set.mm, eliminating *OLD references in 144 proofs. See the Notes entry for 27-Feb-2013.

(21-Feb-2013) *ATTENTION MATHBOX USERS* The order of hypotheses of many syl* theorems were changed, per a suggestion of Mario Carneiro. You need to update your local mathbox copy for compatibility with the new set.mm, or I can do it for you if you wish. See the Notes entry for 21-Feb-2013.

(16-Feb-2013) Scott Fenton shortened the direct-from-axiom proofs of *3.1, *3.43, *4.4, *4.41, *4.5, *4.76, *4.83, *5.33, *5.35, *5.36, and meredith in the "Shortest known proofs of the propositional calculus theorems from Principia Mathematica" (pmproofs.txt).

(27-Jan-2013) Scott Fenton writes, "I've updated Ralph Levien's mmverify.py. It's now a Python 3 program, and supports compressed proofs and file inclusion statements. This adds about fifty lines to the original program. Enjoy!"

(10-Jan-2013) A new mathbox was added for Mario Carneiro, who has contributed a number of cardinality theorems without invoking the Axiom of Choice. This is nice work, and I will be using some of these (those suffixed with "NEW") to replace the existing ones in the main part of set.mm that currently invoke AC unnecessarily.

(4-Jan-2013) As mentioned in the 19-Jun-2012 item below, Eric Schmidt discovered that the complex number axioms axaddcom (now addcom) and ax0id (now addid1) are redundant (schmidt-cnaxioms.pdf, .tex). In addition, ax1id (now mulid1) can be weakened to ax1rid. Scott Fenton has now formalized this work, so that now there are 23 instead of 25 axioms for real and complex numbers in set.mm. The Axioms for Complex Numbers page has been updated with these results. An interesting part of the proof, showing how commutativity of addition follows from other laws, is in addcomi.

(27-Nov-2012) The frequently-used theorems "an1s", "an1rs", "ancom13s", "ancom31s" were renamed to "an12s", "an32s", "an13s", "an31s" to conform to the convention for an12 etc.

(4-Nov-2012) The changes proposed in the Notes, renaming Grp to GrpOp etc., have been incorporated into set.mm. See the list of changes at the top of set.mm. If you want me to update your mathbox with these changes, send it to me along with the version of set.mm that it works with.

(20-Sep-2012) Mel O'Cat updated https://us.metamath.org/ocat/mmj2/TESTmmj2jar.zip. See the README.TXT for a description of the new features.

(21-Aug-2012) Mel O'Cat has uploaded SearchOptionsMockup9.zip, a mockup for the new search screen in mmj2. See the README.txt file for instructions. He will welcome feedback via x178g243 at yahoo.com.

(19-Jun-2012) Eric Schmidt has discovered that in our axioms for complex numbers, axaddcom and ax0id are redundant. (At some point these need to be formalized for set.mm.) He has written up these and some other nice results, including some independence results for the axioms, in schmidt-cnaxioms.pdf (schmidt-cnaxioms.tex).

(23-Apr-2012) Frédéric Liné sent me a PDF (LaTeX source) developed with Lamport's pf2 package. He wrote: "I think it works well with Metamath since the proofs are in a tree form. I use it to have a sketch of a proof. I get this way a better understanding of the proof and I can cut down its size. For instance, inpreima5 was reduced by 50% when I wrote the corresponding proof with pf2."

(5-Mar-2012) I added links to Wikiproofs and its recent changes in the "Wikis" list at the top of this page.

(12-Jan-2012) Thanks to William Hoza who sent me a ZFC T-shirt, and thanks to the ZFC models (courtesy of the Inaccessible Cardinals agency).

FrontBackDetail
ZFC T-shirt front ZFC T-shirt back ZFC T-shirt detail

(24-Nov-2011) In metamath program version 0.07.71, the 'minimize_with' command by default now scans from bottom to top instead of top to bottom, since empirically this often (although not always) results in a shorter proof. A top to bottom scan can be specified with a new qualifier '/reverse'. You can try both methods (starting from the same original proof, of course) and pick the shorter proof.

(15-Oct-2011) From Mel O'Cat:
I just uploaded mmj2.zip containing the 1-Nov-2011 (20111101) release: https://us.metamath.org/ocat/mmj2/mmj2.zip https://us.metamath.org/ocat/mmj2/mmj2.md5
A few last minute tweaks:
1. I now bless double-click starting of mmj2.bat (MacMMJ2.command in Mac OS-X)! See mmj2\QuickStart.html
2. Much improved support of Mac OS-X systems. See mmj2\QuickStart.html
3. I tweaked the Command Line Argument Options report to
a) print every time;
b) print as much as possible even if there are errors in the command line arguments -- and the last line printed corresponds to the argument in error;
c) removed Y/N argument on the command line to enable/disable the report. this simplifies things.
4) Documentation revised, including the PATutorial.
See CHGLOG.TXT for list of all changes. Good luck. And thanks for all of your help!

(15-Sep-2011) MATHBOX USERS: I made a large number of label name changes to set.mm to improve naming consistency. There is a script at the top of the current set.mm that you can use to update your mathbox or older set.mm. Or if you wish, I can do the update on your next mathbox submission - in that case, please include a .zip of the set.mm version you used.

(30-Aug-2011) Scott Fenton shortened the direct-from-axiom proofs of *3.33, *3.45, *4.36, and meredith in the "Shortest known proofs of the propositional calculus theorems from Principia Mathematica" (pmproofs.txt).

(21-Aug-2011) A post on reddit generated 60,000 hits (and a TOS violation notice from my provider...),

(18-Aug-2011) The Metamath Google Group has a discussion of my canonical conjunctions proposal. Any feedback directly to me (Norm Megill) is also welcome.

(4-Jul-2011) John Baker has provided (metamath_kindle.zip) "a modified version of [the] metamath.tex [Metamath] book source that is formatted for the Kindle. If you compile the document the resulting PDF can be loaded into into a Kindle and easily read." (Update: the PDF file is now included also.)

(3-Jul-2011) Nested 'submit' calls are now allowed, in metamath program version 0.07.68. Thus you can create or modify a command file (script) from within a command file then 'submit' it. While 'submit' cannot pass arguments (nor are there plans to add this feature), you can 'substitute' strings in the 'submit' target file before calling it in order to emulate this.

(28-Jun-2011)The metamath program version 0.07.64 adds the '/include_mathboxes' qualifier to 'minimize_with'; by default, 'minimize_with *' will now skip checking user mathboxes. Since mathboxes should be independent from each other, this will help prevent accidental cross-"contamination". Also, '/rewrap' was added to 'write source' to automatically wrap $a and $p comments so as to conform to the current formatting conventions used in set.mm. This means you no longer have to be concerned about line length < 80 etc.

(19-Jun-2011) ATTENTION MATHBOX USERS: The wff variables et, ze, si, and rh are now global. This change was made primarily to resolve some conflicts between mathboxes, but it will also let you avoid having to constantly redeclare these locally in the future. Unfortunately, this change can affect the $f hypothesis order, which can cause proofs referencing theorems that use these variables to fail. All mathbox proofs currently in set.mm have been corrected for this, and you should refresh your local copy for further development of your mathbox. You can correct your proofs that are not in set.mm as follows. Only the proofs that fail under the current set.mm (using version 0.07.62 or later of the metamath program) need to be modified.

To fix a proof that references earlier theorems using et, ze, si, and rh, do the following (using a hypothetical theorem 'abc' as an example): 'prove abc' (ignore error messages), 'delete floating', 'initialize all', 'unify all/interactive', 'improve all', 'save new_proof/compressed'. If your proof uses dummy variables, these must be reassigned manually.

To fix a proof that uses et, ze, si, and rh as local variables, make sure the proof is saved in 'compressed' format. Then delete the local declarations ($v and $f statements) and follow the same steps above to correct the proof.

I apologize for the inconvenience. If you have trouble fixing your proofs, you can contact me for assistance.

Note: Versions of the metamath program before 0.07.62 did not flag an error when global variables were redeclared locally, as it should have according to the spec. This caused these spec violations to go unnoticed in some older set.mm versions. The new error messages are in fact just informational and can be ignored when working with older set.mm versions.

(7-Jun-2011) The metamath program version 0.07.60 fixes a bug with the 'minimize_with' command found by Andrew Salmon.

(12-May-2010) Andrew Salmon shortened many proofs, shown above. For comparison, I have temporarily kept the old version, which is suffixed with OLD, such as oridmOLD for oridm.

(9-Dec-2010) Eric Schmidt has written a Metamath proof verifier in C++, called checkmm.cpp.

(3-Oct-2010) The following changes were made to the tokens in set.mm. The subset and proper subset symbol changes to C_ and C. were made to prevent defeating the parenthesis matching in Emacs. Other changes were made so that all letters a-z and A-Z are now available for variable names. One-letter constants such as _V, _e, and _i are now shown on the web pages with Roman instead of italic font, to disambiguate italic variable names. The new convention is that a prefix of _ indicates Roman font and a prefix of ~ indicates a script (curly) font. Thanks to Stefan Allan and Frédéric Liné for discussions leading to this change.

OldNewDescription
C. _C binomial coefficient
E _E epsilon relation
e _e Euler's constant
I _I identity relation
i _i imaginary unit
V _V universal class
(_ C_ subset
(. C. proper subset
P~ ~P power class
H~ ~H Hilbert space

(25-Sep-2010) The metamath program (version 0.07.54) now implements the current Metamath spec, so footnote 2 on p. 92 of the Metamath book can be ignored.

(24-Sep-2010) The metamath program (version 0.07.53) fixes bug 2106, reported by Michal Burger.

(14-Sep-2010) The metamath program (version 0.07.52) has a revamped LaTeX output with 'show statement xxx /tex', which produces the combined statement, description, and proof similar to the web page generation. Also, 'show proof xxx /lemmon/renumber' now matches the web page step numbers. ('show proof xxx/renumber' still has the indented form conforming to the actual RPN proof, with slightly different numbering.)

(9-Sep-2010) The metamath program (version 0.07.51) was updated with a modification by Stefan Allan that adds hyperlinks the the Ref column of proofs.

(12-Jun-2010) Scott Fenton contributed a D-proof (directly from axioms) of Meredith's single axiom (see the end of pmproofs.txt). A description of Meredith's axiom can be found in theorem meredith.

(11-Jun-2010) A new Metamath mirror was added in Austria, courtesy of Kinder-Enduro.

(28-Feb-2010) Raph Levien's Ghilbert project now has a new Ghilbert site and a Google Group.

(26-Jan-2010) Dmitri Vlasov writes, "I admire the simplicity and power of the metamath language, but still I see its great disadvantage - the proofs in metamath are completely non-manageable by humans without proof assistants. Therefore I decided to develop another language, which would be a higher-level superstructure language towards metamath, and which will support human-readable/writable proofs directly, without proof assistants. I call this language mdl (acronym for 'mathematics development language')." The latest version of Dmitri's translators from metamath to mdl and back can be downloaded from http://mathdevlanguage.sourceforge.net/. Currently only Linux is supported, but Dmitri says is should not be difficult to port it to other platforms that have a g++ compiler.

(11-Sep-2009) The metamath program (version 0.07.48) has been updated to enforce the whitespace requirement of the current spec.

(10-Sep-2009) Matthew Leitch has written an nice article, "How to write mathematics clearly", that briefly mentions Metamath. Overall it makes some excellent points. (I have written to him about a few things I disagree with.)

(28-May-2009) AsteroidMeta is back on-line. Note the URL change.

(12-May-2009) Charles Greathouse wrote a Greasemonkey script to reformat the axiom list on Metamath web site proof pages. This is a beta version; he will appreciate feedback.

(11-May-2009) Stefan Allan modified the metamath program to add the command "show statement xxx /mnemonics", which produces the output file Mnemosyne.txt for use with the Mnemosyne project. The current Metamath program download incorporates this command. Instructions: Create the file mnemosyne.txt with e.g. "show statement ax-* /mnemonics". In the Mnemosyne program, load the file by choosing File->Import then file format "Q and A on separate lines". Notes: (1) Don't try to load all of set.mm, it will crash the program due to a bug in Mnemosyne. (2) On my computer, the arrows in ax-1 don't display. Stefan reports that they do on his computer. (Both are Windows XP.)

(3-May-2009) Steven Baldasty wrote a Metamath syntax highlighting file for the gedit editor. Screenshot.

(1-May-2009) Users on a gaming forum discuss our 2+2=4 proof. Notable comments include "Ew math!" and "Whoever wrote this has absolutely no life."

(12-Mar-2009) Chris Capel has created a Javascript theorem viewer demo that (1) shows substitutions and (2) allows expanding and collapsing proof steps. You are invited to take a look and give him feedback at his Metablog.

(28-Feb-2009) Chris Capel has written a Metamath proof verifier in C#, available at http://pdf23ds.net/bzr/MathEditor/Verifier/Verifier.cs and weighing in at 550 lines. Also, that same URL without the file on it is a Bazaar repository.

(2-Dec-2008) A new section was added to the Deduction Theorem page, called Logic, Metalogic, Metametalogic, and Metametametalogic.

(24-Aug-2008) (From ocat): The 1-Aug-2008 version of mmj2 is ready (mmj2.zip), size = 1,534,041 bytes. This version contains the Theorem Loader enhancement which provides a "sandboxing" capability for user theorems and dynamic update of new theorems to the Metamath database already loaded in memory by mmj2. Also, the new "mmj2 Service" feature enables calling mmj2 as a subroutine, or having mmj2 call your program, and provides access to the mmj2 data structures and objects loaded in memory (i.e. get started writing those Jython programs!) See also mmj2 on AsteroidMeta.

(23-May-2008) Gérard Lang pointed me to Bob Solovay's note on AC and strongly inaccessible cardinals. One of the eventual goals for set.mm is to prove the Axiom of Choice from Grothendieck's axiom, like Mizar does, and this note may be helpful for anyone wanting to attempt that. Separately, I also came across a history of the size reduction of grothprim (viewable in Firefox and some versions of Internet Explorer).

(14-Apr-2008) A "/join" qualifier was added to the "search" command in the metamath program (version 0.07.37). This qualifier will join the $e hypotheses to the $a or $p for searching, so that math tokens in the $e's can be matched as well. For example, "search *com* +v" produces no results, but "search *com* +v /join" yields commutative laws involving vector addition. Thanks to Stefan Allan for suggesting this idea.

(8-Apr-2008) The 8,000th theorem, hlrel, was added to the Metamath Proof Explorer part of the database.

(2-Mar-2008) I added a small section to the end of the Deduction Theorem page.

(17-Feb-2008) ocat has uploaded the "1-Mar-2008" mmj2: mmj2.zip. See the description.

(16-Jan-2008) O'Cat has written mmj2 Proof Assistant Quick Tips.

(30-Dec-2007) "How to build a library of formalized mathematics".

(22-Dec-2007) The Metamath Proof Explorer was included in the top 30 science resources for 2007 by the University at Albany Science Library.

(17-Dec-2007) Metamath's Wikipedia entry says, "This article may require cleanup to meet Wikipedia's quality standards" (see its discussion page). Volunteers are welcome. :) (In the interest of objectivity, I don't edit this entry.)

(20-Nov-2007) Jeff Hoffman created nicod.mm and posted it to the Google Metamath Group.

(19-Nov-2007) Reinder Verlinde suggested adding tooltips to the hyperlinks on the proof pages, which I did for proof step hyperlinks. Discussion.

(5-Nov-2007) A Usenet challenge. :)

(4-Aug-2007) I added a "Request for comments on proposed 'maps to' notation" at the bottom of the AsteroidMeta set.mm discussion page.

(21-Jun-2007) A preprint (PDF file) describing Kurt Maes' axiom of choice with 5 quantifiers, proved in set.mm as ackm.

(20-Jun-2007) The 7,000th theorem, ifpr, was added to the Metamath Proof Explorer part of the database.

(29-Apr-2007) Blog mentions of Metamath: here and here.

(21-Mar-2007) Paul Chapman is working on a new proof browser, which has highlighting that allows you to see the referenced theorem before and after the substitution was made. Here is a screenshot of theorem 0nn0 and a screenshot of theorem 2p2e4.

(15-Mar-2007) A picture of Penny the cat guarding the us.metamath.org server and making the rounds.

(16-Feb-2007) For convenience, the program "drule.c" (pronounced "D-rule", not "drool") mentioned in pmproofs.txt can now be downloaded (drule.c) without having to ask me for it. The same disclaimer applies: even though this program works and has no known bugs, it was not intended for general release. Read the comments at the top of the program for instructions.

(28-Jan-2007) Jason Orendorff set up a new mailing list for Metamath: http://groups.google.com/group/metamath.

(20-Jan-2007) Bob Solovay provided a revised version of his Metamath database for Peano arithmetic, peano.mm.

(2-Jan-2007) Raph Levien has set up a wiki called Barghest for the Ghilbert language and software.

(26-Dec-2006) I posted an explanation of theorem ecoprass on Usenet.

(2-Dec-2006) Berislav Žarnić translated the Metamath Solitaire applet to Croatian.

(26-Nov-2006) Dan Getz has created an RSS feed for new theorems as they appear on this page.

(6-Nov-2006) The first 3 paragraphs in Appendix 2: Note on the Axioms were rewritten to clarify the connection between Tarski's axiom system and Metamath.

(31-Oct-2006) ocat asked for a do-over due to a bug in mmj2 -- if you downloaded the mmj2.zip version dated 10/28/2006, then download the new version dated 10/30.

(29-Oct-2006) ocat has announced that the long-awaited 1-Nov-2006 release of mmj2 is available now.
     The new "Unify+Get Hints" is quite useful, and any proof can be generated as follows. With "?" in the Hyp field and Ref field blank, select "Unify+Get Hints". Select a hint from the list and put it in the Ref field. Edit any $n dummy variables to become the desired wffs. Rinse and repeat for the new proof steps generated, until the proof is done.
     The new tutorial, mmj2PATutorial.bat, explains this in detail. One way to reduce or avoid dummy $n's is to fill in the Hyp field with a comma-separated list of any known hypothesis matches to earlier proof steps, keeping a "?" in the list to indicate that the remaining hypotheses are unknown. Then "Unify+Get Hints" can be applied. The tutorial page \mmj2\data\mmp\PATutorial\Page405.mmp has an example.
     Don't forget that the eimm export/import program lets you go back and forth between the mmj2 and the metamath program proof assistants, without exiting from either one, to exploit the best features of each as required.

(21-Oct-2006) Martin Kiselkov has written a Metamath proof verifier in the Lua scripting language, called verify.lua. While it is not practical as an everyday verifier - he writes that it takes about 40 minutes to verify set.mm on a a Pentium 4 - it could be useful to someone learning Lua or Metamath, and importantly it provides another independent way of verifying the correctness of Metamath proofs. His code looks like it is nicely structured and very readable. He is currently working on a faster version in C++.

(19-Oct-2006) New AsteroidMeta page by Raph, Distinctors_vs_binders.

(13-Oct-2006) I put a simple Metamath browser on my PDA (Palm Tungsten E) so that I don't have to lug around my laptop. Here is a screenshot. It isn't polished, but I'll provide the file + instructions if anyone wants it.

(3-Oct-2006) A blog entry, Principia for Reverse Mathematics.

(28-Sep-2006) A blog entry, Metamath responds.

(26-Sep-2006) A blog entry, Metamath isn't hygienic.

(11-Aug-2006) A blog entry, Metamath and the Peano Induction Axiom.

(26-Jul-2006) A new open problem in predicate calculus was added.

(18-Jun-2006) The 6,000th theorem, mt4d, was added to the Metamath Proof Explorer part of the database.

(9-May-2006) Luca Ciciriello has upgraded the t2mf program, which is a C program used to create the MIDI files on the Metamath Music Page, so that it works on MacOS X. This is a nice accomplishment, since the original program was written before C was standardized by ANSI and will not compile on modern compilers.
      Unfortunately, the original program source states no copyright terms. The main author, Tim Thompson, has kindly agreed to release his code to public domain, but two other authors have also contributed to the code, and so far I have been unable to contact them for copyright clearance. Therefore I cannot offer the MacOS X version for public download on this site until this is resolved. Update 10-May-2006: Another author, M. Czeiszperger, has released his contribution to public domain.
      If you are interested in Luca's modified source code, please contact me directly.

(18-Apr-2006) Incomplete proofs in progress can now be interchanged between the Metamath program's CLI Proof Assistant and mmj2's GUI Proof Assistant, using a new export-import program called eimm. This can be done without exiting either proof assistant, so that the strengths of each approach can be exploited during proof development. See "Use Case 5a" and "Use Case 5b" at mmj2ProofAssistantFeedback.

(28-Mar-2006) Scott Fenton updated his second version of Metamath Solitaire (the one that uses external axioms). He writes: "I've switched to making it a standalone program, as it seems silly to have an applet that can't be run in a web browser. Check the README file for further info." The download is mmsol-0.5.tar.gz.

(27-Mar-2006) Scott Fenton has updated the Metamath Solitaire Java applet to Java 1.5: (1) QSort has been stripped out: its functionality is in the Collections class that Sun ships; (2) all Vectors have been replaced by ArrayLists; (3) generic types have been tossed in wherever they fit: this cuts back drastically on casting; and (4) any warnings Eclipse spouted out have been dealt with. I haven't yet updated it officially, because I don't know if it will work with Microsoft's JVM in older versions of Internet Explorer. The current official version is compiled with Java 1.3, because it won't work with Microsoft's JVM if it is compiled with Java 1.4. (As distasteful as that seems, I will get complaints from users if it doesn't work with Microsoft's JVM.) If anyone can verify that Scott's new version runs on Microsoft's JVM, I would be grateful. Scott's new version is mm.java-1.5.gz; after uncompressing it, rename it to mm.java, use it to replace the existing mm.java file in the Metamath Solitaire download, and recompile according to instructions in the mm.java comments.
      Scott has also created a second version, mmsol-0.2.tar.gz, that reads the axioms from ASCII files, instead of having the axioms hard-coded in the program. This can be very useful if you want to play with custom axioms, and you can also add a collection of starting theorems as "axioms" to work from. However, it must be run from the local directory with appletviewer, since the default Java security model doesn't allow reading files from a browser. It works with the JDK 5 Update 6 Java download.
To compile (from Windows Command Prompt): C:\Program Files\Java\jdk1.5.0_06\bin\javac.exe mm.java
To run (from Windows Command Prompt): C:\Program Files\Java\jdk1.5.0_06\bin\appletviewer.exe mms.html

(21-Jan-2006) Juha Arpiainen proved the independence of axiom ax-11 from the others. This was published as an open problem in my 1995 paper (Remark 9.5 on PDF page 17). See Item 9a on the Workshop Miscellany for his seven-line proof. See also the Asteroid Meta metamathMathQuestions page under the heading "Axiom of variable substitution: ax-11". Congratulations, Juha!

(20-Oct-2005) Juha Arpiainen is working on a proof verifier in Common Lisp called Bourbaki. Its proof language has its roots in Metamath, with the goal of providing a more powerful syntax and definitional soundness checking. See its documentation and related discussion.

(17-Oct-2005) Marnix Klooster has written a Metamath proof verifier in Haskell, called Hmm. Also see his Announcement. The complete program (Hmm.hs, HmmImpl.hs, and HmmVerify.hs) has only 444 lines of code, excluding comments and blank lines. It verifies compressed as well as regular proofs; moreover, it transparently verifies both per-spec compressed proofs and the flawed format he uncovered (see comment below of 16-Oct-05).

(16-Oct-2005) Marnix Klooster noticed that for large proofs, the compressed proof format did not match the spec in the book. His algorithm to correct the problem has been put into the Metamath program (version 0.07.6). The program still verifies older proofs with the incorrect format, but the user will be nagged to update them with 'save proof *'. In set.mm, 285 out of 6376 proofs are affected. (The incorrect format did not affect proof correctness or verification, since the compression and decompression algorithms matched each other.)

(13-Sep-2005) Scott Fenton found an interesting axiom, ax46, which could be used to replace both ax-4 and ax-6.

(29-Jul-2005) Metamath was selected as site of the week by American Scientist Online.

(8-Jul-2005) Roy Longton has contributed 53 new theorems to the Quantum Logic Explorer. You can see them in the Theorem List starting at lem3.3.3lem1. He writes, "If you want, you can post an open challenge to see if anyone can find shorter proofs of the theorems I submitted."

(10-May-2005) A Usenet post I posted about the infinite prime proof; another one about indexed unions.

(3-May-2005) The theorem divexpt is the 5,000th theorem added to the Metamath Proof Explorer database.

(12-Apr-2005) Raph Levien solved the open problem in item 16 on the Workshop Miscellany page and as a corollary proved that axiom ax-9 is independent from the other axioms of predicate calculus and equality. This is the first such independence proof so far; a goal is to prove all of them independent (or to derive any redundant ones from the others).

(8-Mar-2005) I added a paragraph above our complex number axioms table, summarizing the construction and indicating where Dedekind cuts are defined. Thanks to Andrew Buhr for comments on this.

(16-Feb-2005) The Metamath Music Page is mentioned as a reference or resource for a university course called Math, Mind, and Music. .

(28-Jan-2005) Steven Cullinane parodied the Metamath Music Page in his blog.

(18-Jan-2005) Waldek Hebisch upgraded the Metamath program to run on the AMD64 64-bit processor.

(17-Jan-2005) A symbol list summary was added to the beginning of the Hilbert Space Explorer Home Page. Thanks to Mladen Pavicic for suggesting this.

(6-Jan-2005) Someone assembled an amazon.com list of some of the books in the Metamath Proof Explorer Bibliography.

(4-Jan-2005) The definition of ordinal exponentiation was decided on after this Usenet discussion.

(19-Dec-2004) A bit of trivia: my Erdös number is 2, as you can see from this list.

(20-Oct-2004) I started this Usenet discussion about the "reals are uncountable" proof (127 comments; last one on Nov. 12).

(12-Oct-2004) gch-kn shows the equivalence of the Generalized Continuum Hypothesis and Prof. Nambiar's Axiom of Combinatorial Sets. This proof answers his Open Problem 2 (PDF file).

(5-Aug-2004) I gave a talk on "Hilbert Lattice Equations" at the Argonne workshop.

(25-Jul-2004) The theorem nthruz is the 4,000th theorem added to the Metamath Proof Explorer database.

(27-May-2004) Josiah Burroughs contributed the proofs u1lemn1b, u1lem3var1, oi3oa3lem1, and oi3oa3 to the Quantum Logic Explorer database ql.mm.

(23-May-2004) Some minor typos found by Josh Purinton were corrected in the Metamath book. In addition, Josh simplified the definition of the closure of a pre-statement of a formal system in Appendix C.

(5-May-2004) Gregory Bush has found shorter proofs for 67 of the 193 propositional calculus theorems listed in Principia Mathematica, thus establishing 67 new records. (This was challenge #4 on the open problems page.)

  Copyright terms: Public domain W3C HTML validation [external]