HomeHome Metamath Proof Explorer
Theorem List (p. 89 of 425)
< Previous  Next >
Bad symbols? Try the
GIF version.

Mirrors  >  Metamath Home Page  >  MPE Home Page  >  Theorem List Contents  >  Recent Proofs       This page: Page List

Color key:    Metamath Proof Explorer  Metamath Proof Explorer
(1-26947)
  Hilbert Space Explorer  Hilbert Space Explorer
(26948-28472)
  Users' Mathboxes  Users' Mathboxes
(28473-42426)
 

Theorem List for Metamath Proof Explorer - 8801-8900   *Has distinct variable group(s)
TypeLabelDescription
Statement
 
Theoremackbij1lem1 8801 Lemma for ackbij2 8824. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐴𝐵 → (𝐵 ∩ suc 𝐴) = (𝐵𝐴))
 
Theoremackbij1lem2 8802 Lemma for ackbij2 8824. (Contributed by Stefan O'Rear, 18-Nov-2014.)
(𝐴𝐵 → (𝐵 ∩ suc 𝐴) = ({𝐴} ∪ (𝐵𝐴)))
 
Theoremackbij1lem3 8803 Lemma for ackbij2 8824. (Contributed by Stefan O'Rear, 18-Nov-2014.)
(𝐴 ∈ ω → 𝐴 ∈ (𝒫 ω ∩ Fin))
 
Theoremackbij1lem4 8804 Lemma for ackbij2 8824. (Contributed by Stefan O'Rear, 19-Nov-2014.)
(𝐴 ∈ ω → {𝐴} ∈ (𝒫 ω ∩ Fin))
 
Theoremackbij1lem5 8805 Lemma for ackbij2 8824. (Contributed by Stefan O'Rear, 19-Nov-2014.)
(𝐴 ∈ ω → (card‘𝒫 suc 𝐴) = ((card‘𝒫 𝐴) +𝑜 (card‘𝒫 𝐴)))
 
Theoremackbij1lem6 8806 Lemma for ackbij2 8824. (Contributed by Stefan O'Rear, 18-Nov-2014.)
((𝐴 ∈ (𝒫 ω ∩ Fin) ∧ 𝐵 ∈ (𝒫 ω ∩ Fin)) → (𝐴𝐵) ∈ (𝒫 ω ∩ Fin))
 
Theoremackbij1lem7 8807* Lemma for ackbij1 8819. (Contributed by Stefan O'Rear, 21-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))       (𝐴 ∈ (𝒫 ω ∩ Fin) → (𝐹𝐴) = (card‘ 𝑦𝐴 ({𝑦} × 𝒫 𝑦)))
 
Theoremackbij1lem8 8808* Lemma for ackbij1 8819. (Contributed by Stefan O'Rear, 19-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))       (𝐴 ∈ ω → (𝐹‘{𝐴}) = (card‘𝒫 𝐴))
 
Theoremackbij1lem9 8809* Lemma for ackbij1 8819. (Contributed by Stefan O'Rear, 19-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))       ((𝐴 ∈ (𝒫 ω ∩ Fin) ∧ 𝐵 ∈ (𝒫 ω ∩ Fin) ∧ (𝐴𝐵) = ∅) → (𝐹‘(𝐴𝐵)) = ((𝐹𝐴) +𝑜 (𝐹𝐵)))
 
Theoremackbij1lem10 8810* Lemma for ackbij1 8819. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))       𝐹:(𝒫 ω ∩ Fin)⟶ω
 
Theoremackbij1lem11 8811* Lemma for ackbij1 8819. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))       ((𝐴 ∈ (𝒫 ω ∩ Fin) ∧ 𝐵𝐴) → 𝐵 ∈ (𝒫 ω ∩ Fin))
 
Theoremackbij1lem12 8812* Lemma for ackbij1 8819. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))       ((𝐵 ∈ (𝒫 ω ∩ Fin) ∧ 𝐴𝐵) → (𝐹𝐴) ⊆ (𝐹𝐵))
 
Theoremackbij1lem13 8813* Lemma for ackbij1 8819. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))       (𝐹‘∅) = ∅
 
Theoremackbij1lem14 8814* Lemma for ackbij1 8819. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))       (𝐴 ∈ ω → (𝐹‘{𝐴}) = suc (𝐹𝐴))
 
Theoremackbij1lem15 8815* Lemma for ackbij1 8819. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))       (((𝐴 ∈ (𝒫 ω ∩ Fin) ∧ 𝐵 ∈ (𝒫 ω ∩ Fin)) ∧ (𝑐 ∈ ω ∧ 𝑐𝐴 ∧ ¬ 𝑐𝐵)) → ¬ (𝐹‘(𝐴 ∩ suc 𝑐)) = (𝐹‘(𝐵 ∩ suc 𝑐)))
 
Theoremackbij1lem16 8816* Lemma for ackbij1 8819. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))       ((𝐴 ∈ (𝒫 ω ∩ Fin) ∧ 𝐵 ∈ (𝒫 ω ∩ Fin)) → ((𝐹𝐴) = (𝐹𝐵) → 𝐴 = 𝐵))
 
Theoremackbij1lem17 8817* Lemma for ackbij1 8819. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))       𝐹:(𝒫 ω ∩ Fin)–1-1→ω
 
Theoremackbij1lem18 8818* Lemma for ackbij1 8819. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))       (𝐴 ∈ (𝒫 ω ∩ Fin) → ∃𝑏 ∈ (𝒫 ω ∩ Fin)(𝐹𝑏) = suc (𝐹𝐴))
 
Theoremackbij1 8819* The Ackermann bijection, part 1: each natural number can be uniquely coded in binary as a finite set of natural numbers and conversely. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))       𝐹:(𝒫 ω ∩ Fin)–1-1-onto→ω
 
Theoremackbij1b 8820* The Ackermann bijection, part 1b: the bijection from ackbij1 8819 restricts naturally to the powers of particular naturals. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))       (𝐴 ∈ ω → (𝐹 “ 𝒫 𝐴) = (card‘𝒫 𝐴))
 
Theoremackbij2lem2 8821* Lemma for ackbij2 8824. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))    &   𝐺 = (𝑥 ∈ V ↦ (𝑦 ∈ 𝒫 dom 𝑥 ↦ (𝐹‘(𝑥𝑦))))       (𝐴 ∈ ω → (rec(𝐺, ∅)‘𝐴):(𝑅1𝐴)–1-1-onto→(card‘(𝑅1𝐴)))
 
Theoremackbij2lem3 8822* Lemma for ackbij2 8824. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))    &   𝐺 = (𝑥 ∈ V ↦ (𝑦 ∈ 𝒫 dom 𝑥 ↦ (𝐹‘(𝑥𝑦))))       (𝐴 ∈ ω → (rec(𝐺, ∅)‘𝐴) ⊆ (rec(𝐺, ∅)‘suc 𝐴))
 
Theoremackbij2lem4 8823* Lemma for ackbij2 8824. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))    &   𝐺 = (𝑥 ∈ V ↦ (𝑦 ∈ 𝒫 dom 𝑥 ↦ (𝐹‘(𝑥𝑦))))       (((𝐴 ∈ ω ∧ 𝐵 ∈ ω) ∧ 𝐵𝐴) → (rec(𝐺, ∅)‘𝐵) ⊆ (rec(𝐺, ∅)‘𝐴))
 
Theoremackbij2 8824* The Ackermann bijection, part 2: hereditarily finite sets can be represented by recursive binary notation. (Contributed by Stefan O'Rear, 18-Nov-2014.)
𝐹 = (𝑥 ∈ (𝒫 ω ∩ Fin) ↦ (card‘ 𝑦𝑥 ({𝑦} × 𝒫 𝑦)))    &   𝐺 = (𝑥 ∈ V ↦ (𝑦 ∈ 𝒫 dom 𝑥 ↦ (𝐹‘(𝑥𝑦))))    &   𝐻 = (rec(𝐺, ∅) “ ω)       𝐻: (𝑅1 “ ω)–1-1-onto→ω
 
Theoremr1om 8825 The set of hereditarily finite sets is countable. See ackbij2 8824 for an explicit bijection that works without Infinity. See also r1omALT 9353. (Contributed by Stefan O'Rear, 18-Nov-2014.)
(𝑅1‘ω) ≈ ω
 
Theoremfictb 8826 A set is countable iff its collection of finite intersections is countable. (Contributed by Jeff Hankins, 24-Aug-2009.) (Proof shortened by Mario Carneiro, 17-May-2015.)
(𝐴𝐵 → (𝐴 ≼ ω ↔ (fi‘𝐴) ≼ ω))
 
2.6.11  Cofinality (without Axiom of Choice)
 
Theoremcflem 8827* A lemma used to simplify cofinality computations, showing the existence of the cardinal of an unbounded subset of a set 𝐴. (Contributed by NM, 24-Apr-2004.)
(𝐴𝑉 → ∃𝑥𝑦(𝑥 = (card‘𝑦) ∧ (𝑦𝐴 ∧ ∀𝑧𝐴𝑤𝑦 𝑧𝑤)))
 
Theoremcfval 8828* Value of the cofinality function. Definition B of Saharon Shelah, Cardinal Arithmetic (1994), p. xxx (Roman numeral 30). The cofinality of an ordinal number 𝐴 is the cardinality (size) of the smallest unbounded subset 𝑦 of the ordinal number. Unbounded means that for every member of 𝐴, there is a member of 𝑦 that is at least as large. Cofinality is a measure of how "reachable from below" an ordinal is. (Contributed by NM, 1-Apr-2004.) (Revised by Mario Carneiro, 15-Sep-2013.)
(𝐴 ∈ On → (cf‘𝐴) = {𝑥 ∣ ∃𝑦(𝑥 = (card‘𝑦) ∧ (𝑦𝐴 ∧ ∀𝑧𝐴𝑤𝑦 𝑧𝑤))})
 
Theoremcff 8829 Cofinality is a function on the class of ordinal numbers to the class of cardinal numbers. (Contributed by Mario Carneiro, 15-Sep-2013.)
cf:On⟶On
 
Theoremcfub 8830* An upper bound on cofinality. (Contributed by NM, 25-Apr-2004.) (Revised by Mario Carneiro, 15-Sep-2013.)
(cf‘𝐴) ⊆ {𝑥 ∣ ∃𝑦(𝑥 = (card‘𝑦) ∧ (𝑦𝐴𝐴 𝑦))}
 
Theoremcflm 8831* Value of the cofinality function at a limit ordinal. Part of Definition of cofinality of [Enderton] p. 257. (Contributed by NM, 26-Apr-2004.)
((𝐴𝐵 ∧ Lim 𝐴) → (cf‘𝐴) = {𝑥 ∣ ∃𝑦(𝑥 = (card‘𝑦) ∧ (𝑦𝐴𝐴 = 𝑦))})
 
Theoremcf0 8832 Value of the cofinality function at 0. Exercise 2 of [TakeutiZaring] p. 102. (Contributed by NM, 16-Apr-2004.)
(cf‘∅) = ∅
 
Theoremcardcf 8833 Cofinality is a cardinal number. Proposition 11.11 of [TakeutiZaring] p. 103. (Contributed by NM, 24-Apr-2004.) (Revised by Mario Carneiro, 15-Sep-2013.)
(card‘(cf‘𝐴)) = (cf‘𝐴)
 
Theoremcflecard 8834 Cofinality is bounded by the cardinality of its argument. (Contributed by NM, 24-Apr-2004.) (Revised by Mario Carneiro, 15-Sep-2013.)
(cf‘𝐴) ⊆ (card‘𝐴)
 
Theoremcfle 8835 Cofinality is bounded by its argument. Exercise 1 of [TakeutiZaring] p. 102. (Contributed by NM, 26-Apr-2004.) (Revised by Mario Carneiro, 15-Sep-2013.)
(cf‘𝐴) ⊆ 𝐴
 
Theoremcfon 8836 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.)
(cf‘𝐴) ∈ On
 
Theoremcfeq0 8837 Only the ordinal zero has cofinality zero. (Contributed by NM, 24-Apr-2004.) (Revised by Mario Carneiro, 12-Feb-2013.)
(𝐴 ∈ On → ((cf‘𝐴) = ∅ ↔ 𝐴 = ∅))
 
Theoremcfsuc 8838 Value of the cofinality function at a successor ordinal. Exercise 3 of [TakeutiZaring] p. 102. (Contributed by NM, 23-Apr-2004.) (Revised by Mario Carneiro, 12-Feb-2013.)
(𝐴 ∈ On → (cf‘suc 𝐴) = 1𝑜)
 
Theoremcff1 8839* There is always a map from (cf‘𝐴) to 𝐴 (this is a stronger condition than the definition, which only presupposes a map from some 𝑦 ≈ (cf‘𝐴). (Contributed by Mario Carneiro, 28-Feb-2013.)
(𝐴 ∈ On → ∃𝑓(𝑓:(cf‘𝐴)–1-1𝐴 ∧ ∀𝑧𝐴𝑤 ∈ (cf‘𝐴)𝑧 ⊆ (𝑓𝑤)))
 
Theoremcfflb 8840* If there is a cofinal map from 𝐵 to 𝐴, then 𝐵 is at least (cf‘𝐴). This theorem and cff1 8839 motivate the picture of (cf‘𝐴) as the greatest lower bound of the domain of cofinal maps into 𝐴. (Contributed by Mario Carneiro, 28-Feb-2013.)
((𝐴 ∈ On ∧ 𝐵 ∈ On) → (∃𝑓(𝑓:𝐵𝐴 ∧ ∀𝑧𝐴𝑤𝐵 𝑧 ⊆ (𝑓𝑤)) → (cf‘𝐴) ⊆ 𝐵))
 
Theoremcfval2 8841* Another expression for the cofinality function. (Contributed by Mario Carneiro, 28-Feb-2013.)
(𝐴 ∈ On → (cf‘𝐴) = 𝑥 ∈ {𝑥 ∈ 𝒫 𝐴 ∣ ∀𝑧𝐴𝑤𝑥 𝑧𝑤} (card‘𝑥))
 
Theoremcoflim 8842* A simpler expression for the cofinality predicate, at a limit ordinal. (Contributed by Mario Carneiro, 28-Feb-2013.)
((Lim 𝐴𝐵𝐴) → ( 𝐵 = 𝐴 ↔ ∀𝑥𝐴𝑦𝐵 𝑥𝑦))
 
Theoremcflim3 8843* Another expression for the cofinality function. (Contributed by Mario Carneiro, 28-Feb-2013.)
𝐴 ∈ V       (Lim 𝐴 → (cf‘𝐴) = 𝑥 ∈ {𝑥 ∈ 𝒫 𝐴 𝑥 = 𝐴} (card‘𝑥))
 
Theoremcflim2 8844 The cofinality function is a limit ordinal iff its argument is. (Contributed by Mario Carneiro, 28-Feb-2013.) (Revised by Mario Carneiro, 15-Sep-2013.)
𝐴 ∈ V       (Lim 𝐴 ↔ Lim (cf‘𝐴))
 
Theoremcfom 8845 Value of the cofinality function at omega (the set of natural numbers). Exercise 4 of [TakeutiZaring] p. 102. (Contributed by NM, 23-Apr-2004.) (Proof shortened by Mario Carneiro, 11-Jun-2015.)
(cf‘ω) = ω
 
Theoremcfss 8846* There is a cofinal subset of 𝐴 of cardinality (cf‘𝐴). (Contributed by Mario Carneiro, 24-Jun-2013.)
𝐴 ∈ V       (Lim 𝐴 → ∃𝑥(𝑥𝐴𝑥 ≈ (cf‘𝐴) ∧ 𝑥 = 𝐴))
 
Theoremcfslb 8847 Any cofinal subset of 𝐴 is at least as large as (cf‘𝐴). (Contributed by Mario Carneiro, 24-Jun-2013.)
𝐴 ∈ V       ((Lim 𝐴𝐵𝐴 𝐵 = 𝐴) → (cf‘𝐴) ≼ 𝐵)
 
Theoremcfslbn 8848 Any subset of 𝐴 smaller than its cofinality has union less than 𝐴. (This is the contrapositive to cfslb 8847.) (Contributed by Mario Carneiro, 24-Jun-2013.)
𝐴 ∈ V       ((Lim 𝐴𝐵𝐴𝐵 ≺ (cf‘𝐴)) → 𝐵𝐴)
 
Theoremcfslb2n 8849* Any small collection of small subsets of 𝐴 cannot have union 𝐴, where "small" means smaller than the cofinality. This is a stronger version of cfslb 8847. This is a common application of cofinality: under AC, (ℵ‘1) is regular, so it is not a countable union of countable sets. (Contributed by Mario Carneiro, 24-Jun-2013.)
𝐴 ∈ V       ((Lim 𝐴 ∧ ∀𝑥𝐵 (𝑥𝐴𝑥 ≺ (cf‘𝐴))) → (𝐵 ≺ (cf‘𝐴) → 𝐵𝐴))
 
Theoremcofsmo 8850* Any cofinal map implies the existence of a strictly monotone cofinal map with a domain no larger than the original. Proposition 11.7 of [TakeutiZaring] p. 101. (Contributed by Mario Carneiro, 20-Mar-2013.)
𝐶 = {𝑦𝐵 ∣ ∀𝑤𝑦 (𝑓𝑤) ∈ (𝑓𝑦)}    &   𝐾 = {𝑥𝐵𝑧 ⊆ (𝑓𝑥)}    &   𝑂 = OrdIso( E , 𝐶)       ((Ord 𝐴𝐵 ∈ On) → (∃𝑓(𝑓:𝐵𝐴 ∧ ∀𝑧𝐴𝑤𝐵 𝑧 ⊆ (𝑓𝑤)) → ∃𝑥 ∈ suc 𝐵𝑔(𝑔:𝑥𝐴 ∧ Smo 𝑔 ∧ ∀𝑧𝐴𝑣𝑥 𝑧 ⊆ (𝑔𝑣))))
 
Theoremcfsmolem 8851* Lemma for cfsmo 8852. (Contributed by Mario Carneiro, 28-Feb-2013.)
𝐹 = (𝑧 ∈ V ↦ ((𝑔‘dom 𝑧) ∪ 𝑡 ∈ dom 𝑧 suc (𝑧𝑡)))    &   𝐺 = (recs(𝐹) ↾ (cf‘𝐴))       (𝐴 ∈ On → ∃𝑓(𝑓:(cf‘𝐴)⟶𝐴 ∧ Smo 𝑓 ∧ ∀𝑧𝐴𝑤 ∈ (cf‘𝐴)𝑧 ⊆ (𝑓𝑤)))
 
Theoremcfsmo 8852* The map in cff1 8839 can be assumed to be a strictly monotone ordinal function without loss of generality. (Contributed by Mario Carneiro, 28-Feb-2013.)
(𝐴 ∈ On → ∃𝑓(𝑓:(cf‘𝐴)⟶𝐴 ∧ Smo 𝑓 ∧ ∀𝑧𝐴𝑤 ∈ (cf‘𝐴)𝑧 ⊆ (𝑓𝑤)))
 
Theoremcfcoflem 8853* Lemma for cfcof 8855, showing subset relation in one direction. (Contributed by Mario Carneiro, 9-Mar-2013.) (Revised by Mario Carneiro, 26-Dec-2014.)
((𝐴 ∈ On ∧ 𝐵 ∈ On) → (∃𝑓(𝑓:𝐵𝐴 ∧ Smo 𝑓 ∧ ∀𝑥𝐴𝑦𝐵 𝑥 ⊆ (𝑓𝑦)) → (cf‘𝐴) ⊆ (cf‘𝐵)))
 
Theoremcoftr 8854* If there is a cofinal map from 𝐵 to 𝐴 and another from 𝐶 to 𝐴, then there is also a cofinal map from 𝐶 to 𝐵. Proposition 11.9 of [TakeutiZaring] p. 102. A limited form of transitivity for the "cof" relation. This is really a lemma for cfcof 8855. (Contributed by Mario Carneiro, 16-Mar-2013.)
𝐻 = (𝑡𝐶 {𝑛𝐵 ∣ (𝑔𝑡) ⊆ (𝑓𝑛)})       (∃𝑓(𝑓:𝐵𝐴 ∧ Smo 𝑓 ∧ ∀𝑥𝐴𝑦𝐵 𝑥 ⊆ (𝑓𝑦)) → (∃𝑔(𝑔:𝐶𝐴 ∧ ∀𝑧𝐴𝑤𝐶 𝑧 ⊆ (𝑔𝑤)) → ∃(:𝐶𝐵 ∧ ∀𝑠𝐵𝑤𝐶 𝑠 ⊆ (𝑤))))
 
Theoremcfcof 8855* If there is a cofinal map from 𝐴 to 𝐵, then they have the same cofinality. This was used as Definition 11.1 of [TakeutiZaring] p. 100, who defines an equivalence relation cof (𝐴, 𝐵) and defines our cf(𝐵) as the minimum 𝐵 such that cof (𝐴, 𝐵). (Contributed by Mario Carneiro, 20-Mar-2013.)
((𝐴 ∈ On ∧ 𝐵 ∈ On) → (∃𝑓(𝑓:𝐵𝐴 ∧ Smo 𝑓 ∧ ∀𝑧𝐴𝑤𝐵 𝑧 ⊆ (𝑓𝑤)) → (cf‘𝐴) = (cf‘𝐵)))
 
Theoremcfidm 8856 The cofinality function is idempotent. (Contributed by Mario Carneiro, 7-Mar-2013.) (Revised by Mario Carneiro, 15-Sep-2013.)
(cf‘(cf‘𝐴)) = (cf‘𝐴)
 
Theoremalephsing 8857 The cofinality of a limit aleph is the same as the cofinality of its argument, so if (ℵ‘𝐴) < 𝐴, then (ℵ‘𝐴) is singular. Conversely, if (ℵ‘𝐴) is regular (i.e. weakly inaccessible), then (ℵ‘𝐴) = 𝐴, so 𝐴 has to be rather large (see alephfp 8690). Proposition 11.13 of [TakeutiZaring] p. 103. (Contributed by Mario Carneiro, 9-Mar-2013.)
(Lim 𝐴 → (cf‘(ℵ‘𝐴)) = (cf‘𝐴))
 
2.6.12  Eight inequivalent definitions of finite set
 
Theoremsornom 8858* The range of a single-step monotone function from ω into a partially ordered set is a chain. (Contributed by Stefan O'Rear, 3-Nov-2014.)
((𝐹 Fn ω ∧ ∀𝑎 ∈ ω ((𝐹𝑎)𝑅(𝐹‘suc 𝑎) ∨ (𝐹𝑎) = (𝐹‘suc 𝑎)) ∧ 𝑅 Po ran 𝐹) → 𝑅 Or ran 𝐹)
 
Syntaxcfin1a 8859 Extend class notation to include the class of Ia-finite sets.
class FinIa
 
Syntaxcfin2 8860 Extend class notation to include the class of II-finite sets.
class FinII
 
Syntaxcfin4 8861 Extend class notation to include the class of IV-finite sets.
class FinIV
 
Syntaxcfin3 8862 Extend class notation to include the class of III-finite sets.
class FinIII
 
Syntaxcfin5 8863 Extend class notation to include the class of V-finite sets.
class FinV
 
Syntaxcfin6 8864 Extend class notation to include the class of VI-finite sets.
class FinVI
 
Syntaxcfin7 8865 Extend class notation to include the class of VII-finite sets.
class FinVII
 
Definitiondf-fin1a 8866* A set is Ia-finite iff it is not the union of two I-infinite sets. Equivalent to definition Ia of [Levy58] p. 2. A I-infinite Ia-finite set is also known as an amorphous set. This is the second of Levy's eight definitions of finite set. Levy's I-finite is equivalent to our df-fin 7721 and not repeated here. These eight definitions are equivalent with Choice but strictly decreasing in strength in models where Choice fails; conversely, they provide a series of increasingly stronger notions of infiniteness. (Contributed by Stefan O'Rear, 12-Nov-2014.)
FinIa = {𝑥 ∣ ∀𝑦 ∈ 𝒫 𝑥(𝑦 ∈ Fin ∨ (𝑥𝑦) ∈ Fin)}
 
Definitiondf-fin2 8867* A set is II-finite (Tarski finite) iff every nonempty chain of subsets contains a maximum element. Definition II of [Levy58] p. 2. (Contributed by Stefan O'Rear, 12-Nov-2014.)
FinII = {𝑥 ∣ ∀𝑦 ∈ 𝒫 𝒫 𝑥((𝑦 ≠ ∅ ∧ [] Or 𝑦) → 𝑦𝑦)}
 
Definitiondf-fin4 8868* A set is IV-finite (Dedekind finite) iff it has no equinumerous proper subset. Definition IV of [Levy58] p. 3. (Contributed by Stefan O'Rear, 12-Nov-2014.)
FinIV = {𝑥 ∣ ¬ ∃𝑦(𝑦𝑥𝑦𝑥)}
 
Definitiondf-fin3 8869 A set is III-finite (weakly Dedekind finite) iff its power set is Dedekind finite. Definition III of [Levy58] p. 2. (Contributed by Stefan O'Rear, 12-Nov-2014.)
FinIII = {𝑥 ∣ 𝒫 𝑥 ∈ FinIV}
 
Definitiondf-fin5 8870 A set is V-finite iff it behaves finitely under +𝑐. Definition V of [Levy58] p. 3. (Contributed by Stefan O'Rear, 12-Nov-2014.)
FinV = {𝑥 ∣ (𝑥 = ∅ ∨ 𝑥 ≺ (𝑥 +𝑐 𝑥))}
 
Definitiondf-fin6 8871 A set is VI-finite iff it behaves finitely under ×. Definition VI of [Levy58] p. 4. (Contributed by Stefan O'Rear, 12-Nov-2014.)
FinVI = {𝑥 ∣ (𝑥 ≺ 2𝑜𝑥 ≺ (𝑥 × 𝑥))}
 
Definitiondf-fin7 8872* A set is VII-finite iff it cannot be infinitely well-ordered. Equivalent to definition VII of [Levy58] p. 4. (Contributed by Stefan O'Rear, 12-Nov-2014.)
FinVII = {𝑥 ∣ ¬ ∃𝑦 ∈ (On ∖ ω)𝑥𝑦}
 
Theoremisfin1a 8873* Definition of a Ia-finite set. (Contributed by Stefan O'Rear, 16-May-2015.)
(𝐴𝑉 → (𝐴 ∈ FinIa ↔ ∀𝑦 ∈ 𝒫 𝐴(𝑦 ∈ Fin ∨ (𝐴𝑦) ∈ Fin)))
 
Theoremfin1ai 8874 Property of a Ia-finite set. (Contributed by Stefan O'Rear, 16-May-2015.)
((𝐴 ∈ FinIa𝑋𝐴) → (𝑋 ∈ Fin ∨ (𝐴𝑋) ∈ Fin))
 
Theoremisfin2 8875* Definition of a II-finite set. (Contributed by Stefan O'Rear, 16-May-2015.)
(𝐴𝑉 → (𝐴 ∈ FinII ↔ ∀𝑦 ∈ 𝒫 𝒫 𝐴((𝑦 ≠ ∅ ∧ [] Or 𝑦) → 𝑦𝑦)))
 
Theoremfin2i 8876 Property of a II-finite set. (Contributed by Stefan O'Rear, 16-May-2015.)
(((𝐴 ∈ FinII𝐵 ⊆ 𝒫 𝐴) ∧ (𝐵 ≠ ∅ ∧ [] Or 𝐵)) → 𝐵𝐵)
 
Theoremisfin3 8877 Definition of a III-finite set. (Contributed by Stefan O'Rear, 16-May-2015.)
(𝐴 ∈ FinIII ↔ 𝒫 𝐴 ∈ FinIV)
 
Theoremisfin4 8878* Definition of a IV-finite set. (Contributed by Stefan O'Rear, 16-May-2015.)
(𝐴𝑉 → (𝐴 ∈ FinIV ↔ ¬ ∃𝑦(𝑦𝐴𝑦𝐴)))
 
Theoremfin4i 8879 Infer that a set is IV-infinite. (Contributed by Stefan O'Rear, 16-May-2015.)
((𝑋𝐴𝑋𝐴) → ¬ 𝐴 ∈ FinIV)
 
Theoremisfin5 8880 Definition of a V-finite set. (Contributed by Stefan O'Rear, 16-May-2015.)
(𝐴 ∈ FinV ↔ (𝐴 = ∅ ∨ 𝐴 ≺ (𝐴 +𝑐 𝐴)))
 
Theoremisfin6 8881 Definition of a VI-finite set. (Contributed by Stefan O'Rear, 16-May-2015.)
(𝐴 ∈ FinVI ↔ (𝐴 ≺ 2𝑜𝐴 ≺ (𝐴 × 𝐴)))
 
Theoremisfin7 8882* Definition of a VII-finite set. (Contributed by Stefan O'Rear, 16-May-2015.)
(𝐴𝑉 → (𝐴 ∈ FinVII ↔ ¬ ∃𝑦 ∈ (On ∖ ω)𝐴𝑦))
 
Theoremsdom2en01 8883 A set with less than two elements has 0 or 1. (Contributed by Stefan O'Rear, 30-Oct-2014.)
(𝐴 ≺ 2𝑜 ↔ (𝐴 = ∅ ∨ 𝐴 ≈ 1𝑜))
 
Theoreminfpssrlem1 8884 Lemma for infpssr 8889. (Contributed by Stefan O'Rear, 30-Oct-2014.)
(𝜑𝐵𝐴)    &   (𝜑𝐹:𝐵1-1-onto𝐴)    &   (𝜑𝐶 ∈ (𝐴𝐵))    &   𝐺 = (rec(𝐹, 𝐶) ↾ ω)       (𝜑 → (𝐺‘∅) = 𝐶)
 
Theoreminfpssrlem2 8885 Lemma for infpssr 8889. (Contributed by Stefan O'Rear, 30-Oct-2014.)
(𝜑𝐵𝐴)    &   (𝜑𝐹:𝐵1-1-onto𝐴)    &   (𝜑𝐶 ∈ (𝐴𝐵))    &   𝐺 = (rec(𝐹, 𝐶) ↾ ω)       (𝑀 ∈ ω → (𝐺‘suc 𝑀) = (𝐹‘(𝐺𝑀)))
 
Theoreminfpssrlem3 8886 Lemma for infpssr 8889. (Contributed by Stefan O'Rear, 30-Oct-2014.)
(𝜑𝐵𝐴)    &   (𝜑𝐹:𝐵1-1-onto𝐴)    &   (𝜑𝐶 ∈ (𝐴𝐵))    &   𝐺 = (rec(𝐹, 𝐶) ↾ ω)       (𝜑𝐺:ω⟶𝐴)
 
Theoreminfpssrlem4 8887 Lemma for infpssr 8889. (Contributed by Stefan O'Rear, 30-Oct-2014.)
(𝜑𝐵𝐴)    &   (𝜑𝐹:𝐵1-1-onto𝐴)    &   (𝜑𝐶 ∈ (𝐴𝐵))    &   𝐺 = (rec(𝐹, 𝐶) ↾ ω)       ((𝜑𝑀 ∈ ω ∧ 𝑁𝑀) → (𝐺𝑀) ≠ (𝐺𝑁))
 
Theoreminfpssrlem5 8888 Lemma for infpssr 8889. (Contributed by Stefan O'Rear, 30-Oct-2014.)
(𝜑𝐵𝐴)    &   (𝜑𝐹:𝐵1-1-onto𝐴)    &   (𝜑𝐶 ∈ (𝐴𝐵))    &   𝐺 = (rec(𝐹, 𝐶) ↾ ω)       (𝜑 → (𝐴𝑉 → ω ≼ 𝐴))
 
Theoreminfpssr 8889 Dedekind infinity implies existence of a denumerable subset: take a single point witnessing the proper subset relation and iterate the embedding. (Contributed by Stefan O'Rear, 30-Oct-2014.) (Revised by Mario Carneiro, 16-May-2015.)
((𝑋𝐴𝑋𝐴) → ω ≼ 𝐴)
 
Theoremfin4en1 8890 Dedekind finite is a cardinal property. (Contributed by Stefan O'Rear, 30-Oct-2014.) (Revised by Mario Carneiro, 16-May-2015.)
(𝐴𝐵 → (𝐴 ∈ FinIV𝐵 ∈ FinIV))
 
Theoremssfin4 8891 Dedekind finite sets have Dedekind finite subsets. (Contributed by Stefan O'Rear, 30-Oct-2014.) (Revised by Mario Carneiro, 16-May-2015.) (Revised by Mario Carneiro, 6-May-2015.)
((𝐴 ∈ FinIV𝐵𝐴) → 𝐵 ∈ FinIV)
 
Theoremdomfin4 8892 A set dominated by a Dedekind finite set is Dedekind finite. (Contributed by Mario Carneiro, 16-May-2015.)
((𝐴 ∈ FinIV𝐵𝐴) → 𝐵 ∈ FinIV)
 
Theoremominf4 8893 ω is Dedekind infinite. (Contributed by Stefan O'Rear, 30-Oct-2014.) (Proof shortened by Mario Carneiro, 16-May-2015.)
¬ ω ∈ FinIV
 
TheoreminfpssALT 8894* Alternate proof of infpss 8798, shorter but requiring Replacement (ax-rep 4597). (Contributed by Stefan O'Rear, 30-Oct-2014.) (Revised by Mario Carneiro, 16-May-2015.) (Proof modification is discouraged.) (New usage is discouraged.)
(ω ≼ 𝐴 → ∃𝑥(𝑥𝐴𝑥𝐴))
 
Theoremisfin4-2 8895 Alternate definition of IV-finite sets: they lack a denumerable subset. (Contributed by Stefan O'Rear, 30-Oct-2014.) (Revised by Mario Carneiro, 17-May-2015.)
(𝐴𝑉 → (𝐴 ∈ FinIV ↔ ¬ ω ≼ 𝐴))
 
Theoremisfin4-3 8896 Alternate definition of IV-finite sets: they are strictly dominated by their successors. (Thus, the proper subset referred to in isfin4 8878 can be assumed to be only a singleton smaller than the original.) (Contributed by Mario Carneiro, 18-May-2015.)
(𝐴 ∈ FinIV𝐴 ≺ (𝐴 +𝑐 1𝑜))
 
Theoremfin23lem7 8897* Lemma for isfin2-2 8900. The componentwise complement of a nonempty collection of sets is nonempty. (Contributed by Stefan O'Rear, 31-Oct-2014.) (Revised by Mario Carneiro, 16-May-2015.)
((𝐴𝑉𝐵 ⊆ 𝒫 𝐴𝐵 ≠ ∅) → {𝑥 ∈ 𝒫 𝐴 ∣ (𝐴𝑥) ∈ 𝐵} ≠ ∅)
 
Theoremfin23lem11 8898* Lemma for isfin2-2 8900. (Contributed by Stefan O'Rear, 31-Oct-2014.) (Revised by Mario Carneiro, 16-May-2015.)
(𝑧 = (𝐴𝑥) → (𝜓𝜒))    &   (𝑤 = (𝐴𝑣) → (𝜑𝜃))    &   ((𝑥𝐴𝑣𝐴) → (𝜒𝜃))       (𝐵 ⊆ 𝒫 𝐴 → (∃𝑥 ∈ {𝑐 ∈ 𝒫 𝐴 ∣ (𝐴𝑐) ∈ 𝐵}∀𝑤 ∈ {𝑐 ∈ 𝒫 𝐴 ∣ (𝐴𝑐) ∈ 𝐵} ¬ 𝜑 → ∃𝑧𝐵𝑣𝐵 ¬ 𝜓))
 
Theoremfin2i2 8899 A II-finite set contains minimal elements for every nonempty chain. (Contributed by Mario Carneiro, 16-May-2015.)
(((𝐴 ∈ FinII𝐵 ⊆ 𝒫 𝐴) ∧ (𝐵 ≠ ∅ ∧ [] Or 𝐵)) → 𝐵𝐵)
 
Theoremisfin2-2 8900* FinII expressed in terms of minimal elements. (Contributed by Stefan O'Rear, 2-Nov-2014.) (Proof shortened by Mario Carneiro, 16-May-2015.)
(𝐴𝑉 → (𝐴 ∈ FinII ↔ ∀𝑦 ∈ 𝒫 𝒫 𝐴((𝑦 ≠ ∅ ∧ [] Or 𝑦) → 𝑦𝑦)))
    < Previous  Next >

Page List
Jump to page: Contents  1 1-100 2 101-200 3 201-300 4 301-400 5 401-500 6 501-600 7 601-700 8 701-800 9 801-900 10 901-1000 11 1001-1100 12 1101-1200 13 1201-1300 14 1301-1400 15 1401-1500 16 1501-1600 17 1601-1700 18 1701-1800 19 1801-1900 20 1901-2000 21 2001-2100 22 2101-2200 23 2201-2300 24 2301-2400 25 2401-2500 26 2501-2600 27 2601-2700 28 2701-2800 29 2801-2900 30 2901-3000 31 3001-3100 32 3101-3200 33 3201-3300 34 3301-3400 35 3401-3500 36 3501-3600 37 3601-3700 38 3701-3800 39 3801-3900 40 3901-4000 41 4001-4100 42 4101-4200 43 4201-4300 44 4301-4400 45 4401-4500 46 4501-4600 47 4601-4700 48 4701-4800 49 4801-4900 50 4901-5000 51 5001-5100 52 5101-5200 53 5201-5300 54 5301-5400 55 5401-5500 56 5501-5600 57 5601-5700 58 5701-5800 59 5801-5900 60 5901-6000 61 6001-6100 62 6101-6200 63 6201-6300 64 6301-6400 65 6401-6500 66 6501-6600 67 6601-6700 68 6701-6800 69 6801-6900 70 6901-7000 71 7001-7100 72 7101-7200 73 7201-7300 74 7301-7400 75 7401-7500 76 7501-7600 77 7601-7700 78 7701-7800 79 7801-7900 80 7901-8000 81 8001-8100 82 8101-8200 83 8201-8300 84 8301-8400 85 8401-8500 86 8501-8600 87 8601-8700 88 8701-8800 89 8801-8900 90 8901-9000 91 9001-9100 92 9101-9200 93 9201-9300 94 9301-9400 95 9401-9500 96 9501-9600 97 9601-9700 98 9701-9800 99 9801-9900 100 9901-10000 101 10001-10100 102 10101-10200 103 10201-10300 104 10301-10400 105 10401-10500 106 10501-10600 107 10601-10700 108 10701-10800 109 10801-10900 110 10901-11000 111 11001-11100 112 11101-11200 113 11201-11300 114 11301-11400 115 11401-11500 116 11501-11600 117 11601-11700 118 11701-11800 119 11801-11900 120 11901-12000 121 12001-12100 122 12101-12200 123 12201-12300 124 12301-12400 125 12401-12500 126 12501-12600 127 12601-12700 128 12701-12800 129 12801-12900 130 12901-13000 131 13001-13100 132 13101-13200 133 13201-13300 134 13301-13400 135 13401-13500 136 13501-13600 137 13601-13700 138 13701-13800 139 13801-13900 140 13901-14000 141 14001-14100 142 14101-14200 143 14201-14300 144 14301-14400 145 14401-14500 146 14501-14600 147 14601-14700 148 14701-14800 149 14801-14900 150 14901-15000 151 15001-15100 152 15101-15200 153 15201-15300 154 15301-15400 155 15401-15500 156 15501-15600 157 15601-15700 158 15701-15800 159 15801-15900 160 15901-16000 161 16001-16100 162 16101-16200 163 16201-16300 164 16301-16400 165 16401-16500 166 16501-16600 167 16601-16700 168 16701-16800 169 16801-16900 170 16901-17000 171 17001-17100 172 17101-17200 173 17201-17300 174 17301-17400 175 17401-17500 176 17501-17600 177 17601-17700 178 17701-17800 179 17801-17900 180 17901-18000 181 18001-18100 182 18101-18200 183 18201-18300 184 18301-18400 185 18401-18500 186 18501-18600 187 18601-18700 188 18701-18800 189 18801-18900 190 18901-19000 191 19001-19100 192 19101-19200 193 19201-19300 194 19301-19400 195 19401-19500 196 19501-19600 197 19601-19700 198 19701-19800 199 19801-19900 200 19901-20000 201 20001-20100 202 20101-20200 203 20201-20300 204 20301-20400 205 20401-20500 206 20501-20600 207 20601-20700 208 20701-20800 209 20801-20900 210 20901-21000 211 21001-21100 212 21101-21200 213 21201-21300 214 21301-21400 215 21401-21500 216 21501-21600 217 21601-21700 218 21701-21800 219 21801-21900 220 21901-22000 221 22001-22100 222 22101-22200 223 22201-22300 224 22301-22400 225 22401-22500 226 22501-22600 227 22601-22700 228 22701-22800 229 22801-22900 230 22901-23000 231 23001-23100 232 23101-23200 233 23201-23300 234 23301-23400 235 23401-23500 236 23501-23600 237 23601-23700 238 23701-23800 239 23801-23900 240 23901-24000 241 24001-24100 242 24101-24200 243 24201-24300 244 24301-24400 245 24401-24500 246 24501-24600 247 24601-24700 248 24701-24800 249 24801-24900 250 24901-25000 251 25001-25100 252 25101-25200 253 25201-25300 254 25301-25400 255 25401-25500 256 25501-25600 257 25601-25700 258 25701-25800 259 25801-25900 260 25901-26000 261 26001-26100 262 26101-26200 263 26201-26300 264 26301-26400 265 26401-26500 266 26501-26600 267 26601-26700 268 26701-26800 269 26801-26900 270 26901-27000 271 27001-27100 272 27101-27200 273 27201-27300 274 27301-27400 275 27401-27500 276 27501-27600 277 27601-27700 278 27701-27800 279 27801-27900 280 27901-28000 281 28001-28100 282 28101-28200 283 28201-28300 284 28301-28400 285 28401-28500 286 28501-28600 287 28601-28700 288 28701-28800 289 28801-28900 290 28901-29000 291 29001-29100 292 29101-29200 293 29201-29300 294 29301-29400 295 29401-29500 296 29501-29600 297 29601-29700 298 29701-29800 299 29801-29900 300 29901-30000 301 30001-30100 302 30101-30200 303 30201-30300 304 30301-30400 305 30401-30500 306 30501-30600 307 30601-30700 308 30701-30800 309 30801-30900 310 30901-31000 311 31001-31100 312 31101-31200 313 31201-31300 314 31301-31400 315 31401-31500 316 31501-31600 317 31601-31700 318 31701-31800 319 31801-31900 320 31901-32000 321 32001-32100 322 32101-32200 323 32201-32300 324 32301-32400 325 32401-32500 326 32501-32600 327 32601-32700 328 32701-32800 329 32801-32900 330 32901-33000 331 33001-33100 332 33101-33200 333 33201-33300 334 33301-33400 335 33401-33500 336 33501-33600 337 33601-33700 338 33701-33800 339 33801-33900 340 33901-34000 341 34001-34100 342 34101-34200 343 34201-34300 344 34301-34400 345 34401-34500 346 34501-34600 347 34601-34700 348 34701-34800 349 34801-34900 350 34901-35000 351 35001-35100 352 35101-35200 353 35201-35300 354 35301-35400 355 35401-35500 356 35501-35600 357 35601-35700 358 35701-35800 359 35801-35900 360 35901-36000 361 36001-36100 362 36101-36200 363 36201-36300 364 36301-36400 365 36401-36500 366 36501-36600 367 36601-36700 368 36701-36800 369 36801-36900 370 36901-37000 371 37001-37100 372 37101-37200 373 37201-37300 374 37301-37400 375 37401-37500 376 37501-37600 377 37601-37700 378 37701-37800 379 37801-37900 380 37901-38000 381 38001-38100 382 38101-38200 383 38201-38300 384 38301-38400 385 38401-38500 386 38501-38600 387 38601-38700 388 38701-38800 389 38801-38900 390 38901-39000 391 39001-39100 392 39101-39200 393 39201-39300 394 39301-39400 395 39401-39500 396 39501-39600 397 39601-39700 398 39701-39800 399 39801-39900 400 39901-40000 401 40001-40100 402 40101-40200 403 40201-40300 404 40301-40400 405 40401-40500 406 40501-40600 407 40601-40700 408 40701-40800 409 40801-40900 410 40901-41000 411 41001-41100 412 41101-41200 413 41201-41300 414 41301-41400 415 41401-41500 416 41501-41600 417 41601-41700 418 41701-41800 419 41801-41900 420 41901-42000 421 42001-42100 422 42101-42200 423 42201-42300 424 42301-42400 425 42401-42426
  Copyright terms: Public domain < Previous  Next >