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Type | Label | Description |
---|---|---|
Statement | ||
Theorem | bj-tagex 34301 | A class is a set if and only if its tagging is a set. (Contributed by BJ, 6-Oct-2018.) |
⊢ (𝐴 ∈ V ↔ tag 𝐴 ∈ V) | ||
Theorem | bj-xtageq 34302 | The products of a given class and the tagging of either of two equal classes are equal. (Contributed by BJ, 6-Apr-2019.) |
⊢ (𝐴 = 𝐵 → (𝐶 × tag 𝐴) = (𝐶 × tag 𝐵)) | ||
Theorem | bj-xtagex 34303 | The product of a set and the tagging of a set is a set. (Contributed by BJ, 2-Apr-2019.) |
⊢ (𝐴 ∈ 𝑉 → (𝐵 ∈ 𝑊 → (𝐴 × tag 𝐵) ∈ V)) | ||
This subsection gives a definition of an ordered pair, or couple (2-tuple), that "works" for proper classes, as evidenced by Theorems bj-2uplth 34335 and bj-2uplex 34336, and more importantly, bj-pr21val 34327 and bj-pr22val 34333. In particular, one can define well-behaved tuples of classes. Classes in ZF(C) are only virtual, and in particular they cannot be quantified over. Theorem bj-2uplex 34336 has advantages: in view of df-br 5069, several sethood antecedents could be removed from existing theorems. For instance, relsnopg 5678 (resp. relsnop 5680) would hold without antecedents (resp. hypotheses) thanks to relsnb 5677). Also, the antecedent Rel 𝑅 could be removed from brrelex12 5606 and related theorems brrelex*, and, as a consequence, of multiple later theorems. Similarly, df-struct 16487 could be simplified by removing the exception currently made for the empty set. The projections are denoted by pr1 and pr2 and the couple with projections (or coordinates) 𝐴 and 𝐵 is denoted by ⦅𝐴, 𝐵⦆. Note that this definition uses the Kuratowksi definition (df-op 4576) as a preliminary definition, and then "redefines" a couple. It could also use the "short" version of the Kuratowski pair (see opthreg 9083) without needing the axiom of regularity; it could even bypass this definition by "inlining" it. This definition is due to Anthony Morse and is expounded (with idiosyncratic notation) in Anthony P. Morse, A Theory of Sets, Academic Press, 1965 (second edition 1986). Note that this extends in a natural way to tuples. A variation of this definition is justified in opthprc 5618, but here we use "tagged versions" of the factors (see df-bj-tag 34289) so that an m-tuple can equal an n-tuple only when m = n (and the projections are the same). A comparison of the different definitions of tuples (strangely not mentioning Morse's), is given in Dominic McCarty and Dana Scott, Reconsidering ordered pairs, Bull. Symbolic Logic, Volume 14, Issue 3 (Sept. 2008), 379--397. where a recursive definition of tuples is given that avoids the 2-step definition of tuples and that can be adapted to various set theories. Finally, another survey is Akihiro Kanamori, The empty set, the singleton, and the ordered pair, Bull. Symbolic Logic, Volume 9, Number 3 (Sept. 2003), 273--298. (available at http://math.bu.edu/people/aki/8.pdf 34289) | ||
Syntax | bj-cproj 34304 | Syntax for the class projection. (Contributed by BJ, 6-Apr-2019.) |
class (𝐴 Proj 𝐵) | ||
Definition | df-bj-proj 34305* | Definition of the class projection corresponding to tagged tuples. The expression (𝐴 Proj 𝐵) denotes the projection on the A^th component. (Contributed by BJ, 6-Apr-2019.) (New usage is discouraged.) |
⊢ (𝐴 Proj 𝐵) = {𝑥 ∣ {𝑥} ∈ (𝐵 “ {𝐴})} | ||
Theorem | bj-projeq 34306 | Substitution property for Proj. (Contributed by BJ, 6-Apr-2019.) |
⊢ (𝐴 = 𝐶 → (𝐵 = 𝐷 → (𝐴 Proj 𝐵) = (𝐶 Proj 𝐷))) | ||
Theorem | bj-projeq2 34307 | Substitution property for Proj. (Contributed by BJ, 6-Apr-2019.) |
⊢ (𝐵 = 𝐶 → (𝐴 Proj 𝐵) = (𝐴 Proj 𝐶)) | ||
Theorem | bj-projun 34308 | The class projection on a given component preserves unions. (Contributed by BJ, 6-Apr-2019.) |
⊢ (𝐴 Proj (𝐵 ∪ 𝐶)) = ((𝐴 Proj 𝐵) ∪ (𝐴 Proj 𝐶)) | ||
Theorem | bj-projex 34309 | Sethood of the class projection. (Contributed by BJ, 6-Apr-2019.) |
⊢ (𝐵 ∈ 𝑉 → (𝐴 Proj 𝐵) ∈ V) | ||
Theorem | bj-projval 34310 | Value of the class projection. (Contributed by BJ, 6-Apr-2019.) |
⊢ (𝐴 ∈ 𝑉 → (𝐴 Proj ({𝐵} × tag 𝐶)) = if(𝐵 = 𝐴, 𝐶, ∅)) | ||
Syntax | bj-c1upl 34311 | Syntax for Morse monuple. (Contributed by BJ, 6-Apr-2019.) |
class ⦅𝐴⦆ | ||
Definition | df-bj-1upl 34312 | Definition of the Morse monuple (1-tuple). This is not useful per se, but is used as a step towards the definition of couples (2-tuples, or ordered pairs). The reason for "tagging" the set is so that an m-tuple and an n-tuple be equal only when m = n. Note that with this definition, the 0-tuple is the empty set. New usage is discouraged because the precise definition is generally unimportant compared to the characteristic properties bj-2upleq 34326, bj-2uplth 34335, bj-2uplex 34336, and the properties of the projections (see df-bj-pr1 34315 and df-bj-pr2 34329). (Contributed by BJ, 6-Apr-2019.) (New usage is discouraged.) |
⊢ ⦅𝐴⦆ = ({∅} × tag 𝐴) | ||
Theorem | bj-1upleq 34313 | Substitution property for ⦅ − ⦆. (Contributed by BJ, 6-Apr-2019.) |
⊢ (𝐴 = 𝐵 → ⦅𝐴⦆ = ⦅𝐵⦆) | ||
Syntax | bj-cpr1 34314 | Syntax for the first class tuple projection. (Contributed by BJ, 6-Apr-2019.) |
class pr1 𝐴 | ||
Definition | df-bj-pr1 34315 | Definition of the first projection of a class tuple. New usage is discouraged because the precise definition is generally unimportant compared to the characteristic properties bj-pr1eq 34316, bj-pr11val 34319, bj-pr21val 34327, bj-pr1ex 34320. (Contributed by BJ, 6-Apr-2019.) (New usage is discouraged.) |
⊢ pr1 𝐴 = (∅ Proj 𝐴) | ||
Theorem | bj-pr1eq 34316 | Substitution property for pr1. (Contributed by BJ, 6-Apr-2019.) |
⊢ (𝐴 = 𝐵 → pr1 𝐴 = pr1 𝐵) | ||
Theorem | bj-pr1un 34317 | The first projection preserves unions. (Contributed by BJ, 6-Apr-2019.) |
⊢ pr1 (𝐴 ∪ 𝐵) = (pr1 𝐴 ∪ pr1 𝐵) | ||
Theorem | bj-pr1val 34318 | Value of the first projection. (Contributed by BJ, 6-Apr-2019.) |
⊢ pr1 ({𝐴} × tag 𝐵) = if(𝐴 = ∅, 𝐵, ∅) | ||
Theorem | bj-pr11val 34319 | Value of the first projection of a monuple. (Contributed by BJ, 6-Apr-2019.) |
⊢ pr1 ⦅𝐴⦆ = 𝐴 | ||
Theorem | bj-pr1ex 34320 | Sethood of the first projection. (Contributed by BJ, 6-Oct-2018.) |
⊢ (𝐴 ∈ 𝑉 → pr1 𝐴 ∈ V) | ||
Theorem | bj-1uplth 34321 | The characteristic property of monuples. Note that this holds without sethood hypotheses. (Contributed by BJ, 6-Apr-2019.) |
⊢ (⦅𝐴⦆ = ⦅𝐵⦆ ↔ 𝐴 = 𝐵) | ||
Theorem | bj-1uplex 34322 | A monuple is a set if and only if its coordinates are sets. (Contributed by BJ, 6-Apr-2019.) |
⊢ (⦅𝐴⦆ ∈ V ↔ 𝐴 ∈ V) | ||
Theorem | bj-1upln0 34323 | A monuple is nonempty. (Contributed by BJ, 6-Apr-2019.) |
⊢ ⦅𝐴⦆ ≠ ∅ | ||
Syntax | bj-c2uple 34324 | Syntax for Morse couple. (Contributed by BJ, 6-Oct-2018.) |
class ⦅𝐴, 𝐵⦆ | ||
Definition | df-bj-2upl 34325 | Definition of the Morse couple. See df-bj-1upl 34312. New usage is discouraged because the precise definition is generally unimportant compared to the characteristic properties bj-2upleq 34326, bj-2uplth 34335, bj-2uplex 34336, and the properties of the projections (see df-bj-pr1 34315 and df-bj-pr2 34329). (Contributed by BJ, 6-Oct-2018.) (New usage is discouraged.) |
⊢ ⦅𝐴, 𝐵⦆ = (⦅𝐴⦆ ∪ ({1o} × tag 𝐵)) | ||
Theorem | bj-2upleq 34326 | Substitution property for ⦅ − , − ⦆. (Contributed by BJ, 6-Oct-2018.) |
⊢ (𝐴 = 𝐵 → (𝐶 = 𝐷 → ⦅𝐴, 𝐶⦆ = ⦅𝐵, 𝐷⦆)) | ||
Theorem | bj-pr21val 34327 | Value of the first projection of a couple. (Contributed by BJ, 6-Oct-2018.) |
⊢ pr1 ⦅𝐴, 𝐵⦆ = 𝐴 | ||
Syntax | bj-cpr2 34328 | Syntax for the second class tuple projection. (Contributed by BJ, 6-Oct-2018.) |
class pr2 𝐴 | ||
Definition | df-bj-pr2 34329 | Definition of the second projection of a class tuple. New usage is discouraged because the precise definition is generally unimportant compared to the characteristic properties bj-pr2eq 34330, bj-pr22val 34333, bj-pr2ex 34334. (Contributed by BJ, 6-Oct-2018.) (New usage is discouraged.) |
⊢ pr2 𝐴 = (1o Proj 𝐴) | ||
Theorem | bj-pr2eq 34330 | Substitution property for pr2. (Contributed by BJ, 6-Oct-2018.) |
⊢ (𝐴 = 𝐵 → pr2 𝐴 = pr2 𝐵) | ||
Theorem | bj-pr2un 34331 | The second projection preserves unions. (Contributed by BJ, 6-Apr-2019.) |
⊢ pr2 (𝐴 ∪ 𝐵) = (pr2 𝐴 ∪ pr2 𝐵) | ||
Theorem | bj-pr2val 34332 | Value of the second projection. (Contributed by BJ, 6-Apr-2019.) |
⊢ pr2 ({𝐴} × tag 𝐵) = if(𝐴 = 1o, 𝐵, ∅) | ||
Theorem | bj-pr22val 34333 | Value of the second projection of a couple. (Contributed by BJ, 6-Oct-2018.) |
⊢ pr2 ⦅𝐴, 𝐵⦆ = 𝐵 | ||
Theorem | bj-pr2ex 34334 | Sethood of the second projection. (Contributed by BJ, 6-Oct-2018.) |
⊢ (𝐴 ∈ 𝑉 → pr2 𝐴 ∈ V) | ||
Theorem | bj-2uplth 34335 | The characteristic property of couples. Note that this holds without sethood hypotheses (compare opth 5370). (Contributed by BJ, 6-Oct-2018.) |
⊢ (⦅𝐴, 𝐵⦆ = ⦅𝐶, 𝐷⦆ ↔ (𝐴 = 𝐶 ∧ 𝐵 = 𝐷)) | ||
Theorem | bj-2uplex 34336 | A couple is a set if and only if its coordinates are sets. For the advantages offered by the reverse closure property, see the section head comment. (Contributed by BJ, 6-Oct-2018.) |
⊢ (⦅𝐴, 𝐵⦆ ∈ V ↔ (𝐴 ∈ V ∧ 𝐵 ∈ V)) | ||
Theorem | bj-2upln0 34337 | A couple is nonempty. (Contributed by BJ, 21-Apr-2019.) |
⊢ ⦅𝐴, 𝐵⦆ ≠ ∅ | ||
Theorem | bj-2upln1upl 34338 | A couple is never equal to a monuple. It is in order to have this "non-clashing" result that tagging was used. Without tagging, we would have ⦅𝐴, ∅⦆ = ⦅𝐴⦆. Note that in the context of Morse tuples, it is natural to define the 0-tuple as the empty set. Therefore, the present theorem together with bj-1upln0 34323 and bj-2upln0 34337 tell us that an m-tuple may equal an n-tuple only when m = n, at least for m, n <= 2, but this result would extend as soon as we define n-tuples for higher values of n. (Contributed by BJ, 21-Apr-2019.) |
⊢ ⦅𝐴, 𝐵⦆ ≠ ⦅𝐶⦆ | ||
Some elementary set-theoretic operations "relative to a universe" (by which is merely meant some given class considered as a universe). | ||
Theorem | bj-rcleqf 34339 | Relative version of cleqf 3012. (Contributed by BJ, 27-Dec-2023.) |
⊢ Ⅎ𝑥𝐴 & ⊢ Ⅎ𝑥𝐵 & ⊢ Ⅎ𝑥𝑉 ⇒ ⊢ ((𝑉 ∩ 𝐴) = (𝑉 ∩ 𝐵) ↔ ∀𝑥 ∈ 𝑉 (𝑥 ∈ 𝐴 ↔ 𝑥 ∈ 𝐵)) | ||
Theorem | bj-rcleq 34340* | Relative version of dfcleq 2817. (Contributed by BJ, 27-Dec-2023.) |
⊢ ((𝑉 ∩ 𝐴) = (𝑉 ∩ 𝐵) ↔ ∀𝑥 ∈ 𝑉 (𝑥 ∈ 𝐴 ↔ 𝑥 ∈ 𝐵)) | ||
Theorem | bj-reabeq 34341* | Relative form of abeq2 2947. (Contributed by BJ, 27-Dec-2023.) |
⊢ ((𝑉 ∩ 𝐴) = {𝑥 ∈ 𝑉 ∣ 𝜑} ↔ ∀𝑥 ∈ 𝑉 (𝑥 ∈ 𝐴 ↔ 𝜑)) | ||
Theorem | bj-disj2r 34342 | Relative version of ssdifin0 4433, allowing a biconditional, and of disj2 4409. (Contributed by BJ, 11-Nov-2021.) This proof does not rely, even indirectly, on ssdifin0 4433 nor disj2 4409. (Proof modification is discouraged.) |
⊢ ((𝐴 ∩ 𝑉) ⊆ (𝑉 ∖ 𝐵) ↔ ((𝐴 ∩ 𝐵) ∩ 𝑉) = ∅) | ||
Theorem | bj-sscon 34343 | Contraposition law for relative subclasses. Relative and generalized version of ssconb 4116, which it can shorten, as well as conss2 40782. (Contributed by BJ, 11-Nov-2021.) This proof does not rely, even indirectly, on ssconb 4116 nor conss2 40782. (Proof modification is discouraged.) |
⊢ ((𝐴 ∩ 𝑉) ⊆ (𝑉 ∖ 𝐵) ↔ (𝐵 ∩ 𝑉) ⊆ (𝑉 ∖ 𝐴)) | ||
Miscellaneous theorems of set theory. | ||
Theorem | bj-pw0ALT 34344 | Alternate proof of pw0 4747. The proofs have a similar structure: pw0 4747 uses the definitions of powerclass and singleton as class abstractions, whereas bj-pw0ALT 34344 uses characterizations of their elements. Both proofs then use transitivity of a congruence relation (equality for pw0 4747 and biconditional for bj-pw0ALT 34344) to translate the property ss0b 4353 into the wanted result. To translate a biconditional into a class equality, pw0 4747 uses abbii 2888 (which yields an equality of class abstractions), while bj-pw0ALT 34344 uses eqriv 2820 (which requires a biconditional of membership of a given setvar variable). Note that abbii 2888, through its closed form abbi1 2886, is proved from eqrdv 2821, which is the deduction form of eqriv 2820. In the other direction, velpw 4546 and velsn 4585 are proved from the definitions of powerclass and singleton using elabg 3668, which is a version of abbii 2888 suited for membership characterizations. (Contributed by BJ, 14-Apr-2024.) (Proof modification is discouraged.) (New usage is discouraged.) |
⊢ 𝒫 ∅ = {∅} | ||
Theorem | bj-sselpwuni 34345 | Quantitative version of ssexg 5229: a subset of an element of a class is an element of the powerclass of the union of that class. (Contributed by BJ, 6-Apr-2024.) |
⊢ ((𝐴 ⊆ 𝐵 ∧ 𝐵 ∈ 𝑉) → 𝐴 ∈ 𝒫 ∪ 𝑉) | ||
Theorem | bj-unirel 34346 | Quantitative version of uniexr 7487: if the union of a class is an element of a class, then that class is an element of the double powerclass of the union of this class. (Contributed by BJ, 6-Apr-2024.) |
⊢ (∪ 𝐴 ∈ 𝑉 → 𝐴 ∈ 𝒫 𝒫 ∪ 𝑉) | ||
Theorem | bj-elpwg 34347 | If the intersection of two classes is a set, then inclusion among these classes is equivalent to membership in the powerclass. Common generalization of elpwg 4544 and elpw2g 5249 (the latter of which could be proved from it). (Contributed by BJ, 31-Dec-2023.) |
⊢ ((𝐴 ∩ 𝐵) ∈ 𝑉 → (𝐴 ∈ 𝒫 𝐵 ↔ 𝐴 ⊆ 𝐵)) | ||
Theorem | bj-vjust 34348 | Justification theorem for bj-df-v 34349. See also vjust 3497. (Contributed by BJ, 30-Nov-2019.) (Proof modification is discouraged.) |
⊢ {𝑥 ∣ ⊤} = {𝑦 ∣ ⊤} | ||
Theorem | bj-df-v 34349 | Alternate definition of the universal class. Actually, the current definition df-v 3498 should be proved from this one, and vex 3499 should be proved from this proposed definition together with vexw 2807, which would remove from vex 3499 dependency on ax-13 2390 (see also comment of vexw 2807). (Contributed by BJ, 30-Nov-2019.) (Proof modification is discouraged.) |
⊢ V = {𝑥 ∣ ⊤} | ||
Theorem | bj-df-nul 34350 | Alternate definition of the empty class/set. (Contributed by BJ, 30-Nov-2019.) (Proof modification is discouraged.) |
⊢ ∅ = {𝑥 ∣ ⊥} | ||
Theorem | bj-nul 34351* | Two formulations of the axiom of the empty set ax-nul 5212. Proposal: place it right before ax-nul 5212. (Contributed by BJ, 30-Nov-2019.) (Proof modification is discouraged.) |
⊢ (∅ ∈ V ↔ ∃𝑥∀𝑦 ¬ 𝑦 ∈ 𝑥) | ||
Theorem | bj-nuliota 34352* | Definition of the empty set using the definite description binder. See also bj-nuliotaALT 34353. (Contributed by BJ, 30-Nov-2019.) (Proof modification is discouraged.) |
⊢ ∅ = (℩𝑥∀𝑦 ¬ 𝑦 ∈ 𝑥) | ||
Theorem | bj-nuliotaALT 34353* | Alternate proof of bj-nuliota 34352. Note that this alternate proof uses the fact that ℩𝑥𝜑 evaluates to ∅ when there is no 𝑥 satisfying 𝜑 (iotanul 6335). This is an implementation detail of the encoding currently used in set.mm and should be avoided. (Contributed by BJ, 30-Nov-2019.) (Proof modification is discouraged.) (New usage is discouraged.) |
⊢ ∅ = (℩𝑥∀𝑦 ¬ 𝑦 ∈ 𝑥) | ||
Theorem | bj-vtoclgfALT 34354 | Alternate proof of vtoclgf 3567. Proof from vtoclgft 3555. (This may have been the original proof before shortening.) (Contributed by BJ, 30-Sep-2019.) (Proof modification is discouraged.) (New usage is discouraged.) |
⊢ Ⅎ𝑥𝐴 & ⊢ Ⅎ𝑥𝜓 & ⊢ (𝑥 = 𝐴 → (𝜑 ↔ 𝜓)) & ⊢ 𝜑 ⇒ ⊢ (𝐴 ∈ 𝑉 → 𝜓) | ||
Theorem | bj-elsn12g 34355 | Join of elsng 4583 and elsn2g 4605. (Contributed by BJ, 18-Nov-2023.) |
⊢ ((𝐴 ∈ 𝑉 ∨ 𝐵 ∈ 𝑊) → (𝐴 ∈ {𝐵} ↔ 𝐴 = 𝐵)) | ||
Theorem | bj-elsnb 34356 | Biconditional version of elsng 4583. (Contributed by BJ, 18-Nov-2023.) |
⊢ (𝐴 ∈ {𝐵} ↔ (𝐴 ∈ V ∧ 𝐴 = 𝐵)) | ||
Theorem | bj-pwcfsdom 34357 | Remove hypothesis from pwcfsdom 10007. Illustration of how to remove a "proof-facilitating hypothesis". (Can use it to shorten theorems using pwcfsdom 10007.) (Contributed by BJ, 14-Sep-2019.) |
⊢ (ℵ‘𝐴) ≺ ((ℵ‘𝐴) ↑m (cf‘(ℵ‘𝐴))) | ||
Theorem | bj-grur1 34358 | Remove hypothesis from grur1 10244. Illustration of how to remove a "definitional hypothesis". This makes its uses longer, but the theorem feels more self-contained. It looks preferable when the defined term appears only once in the conclusion. (Contributed by BJ, 14-Sep-2019.) |
⊢ ((𝑈 ∈ Univ ∧ 𝑈 ∈ ∪ (𝑅1 “ On)) → 𝑈 = (𝑅1‘(𝑈 ∩ On))) | ||
Theorem | bj-bm1.3ii 34359* |
The extension of a predicate (𝜑(𝑧)) is included in a set
(𝑥) if and only if it is a set (𝑦).
Sufficiency is obvious,
and necessity is the content of the axiom of separation ax-sep 5205.
Similar to Theorem 1.3(ii) of [BellMachover] p. 463. (Contributed by
NM, 21-Jun-1993.) Generalized to a closed form biconditional with
existential quantifications using two different setvars 𝑥, 𝑦 (which
need not be disjoint). (Revised by BJ, 8-Aug-2022.)
TODO: move in place of bm1.3ii 5208. Relabel ("sepbi"?). |
⊢ (∃𝑥∀𝑧(𝜑 → 𝑧 ∈ 𝑥) ↔ ∃𝑦∀𝑧(𝑧 ∈ 𝑦 ↔ 𝜑)) | ||
Theorem | bj-0nelopab 34360 |
The empty set is never an element in an ordered-pair class abstraction.
(Contributed by Alexander van der Vekens, 5-Nov-2017.) (Proof shortened
by BJ, 22-Jul-2023.)
TODO: move to the main section when one can reorder sections so that we can use relopab 5698 (this is a very limited reordering). |
⊢ ¬ ∅ ∈ {〈𝑥, 𝑦〉 ∣ 𝜑} | ||
Theorem | bj-brrelex12ALT 34361 | Two classes related by a binary relation are both sets. Alternate proof of brrelex12 5606. (Contributed by BJ, 14-Jul-2023.) (Proof modification is discouraged.) (New usage is discouraged.) |
⊢ ((Rel 𝑅 ∧ 𝐴𝑅𝐵) → (𝐴 ∈ V ∧ 𝐵 ∈ V)) | ||
Theorem | bj-epelg 34362 | The membership relation and the membership predicate agree when the "containing" class is a set. General version of epel 5471 and closed form of epeli 5470. (Contributed by Scott Fenton, 27-Mar-2011.) (Revised by Mario Carneiro, 28-Apr-2015.) TODO: move it to the main section after reordering to have brrelex1i 5610 available. (Proof shortened by BJ, 14-Jul-2023.) (Proof modification is discouraged.) |
⊢ (𝐵 ∈ 𝑉 → (𝐴 E 𝐵 ↔ 𝐴 ∈ 𝐵)) | ||
Theorem | bj-epelb 34363 | Two classes are related by the membership relation if and only if they are related by the membership relation (i.e., the first is an element of the second) and the second is a set (hence so is the first). TODO: move to Main after reordering to have brrelex2i 5611 available. Check if it is shorter to prove bj-epelg 34362 first or bj-epelb 34363 first. (Contributed by BJ, 14-Jul-2023.) |
⊢ (𝐴 E 𝐵 ↔ (𝐴 ∈ 𝐵 ∧ 𝐵 ∈ V)) | ||
Theorem | bj-nsnid 34364 | A set does not contain the singleton formed on it. More precisely, one can prove that a class contains the singleton formed on it if and only if it is proper and contains the empty set (since it is "the singleton formed on" any proper class, see snprc 4655): ⊢ ¬ ({𝐴} ∈ 𝐴 ↔ (∅ ∈ 𝐴 → 𝐴 ∈ V)). (Contributed by BJ, 4-Feb-2023.) |
⊢ (𝐴 ∈ 𝑉 → ¬ {𝐴} ∈ 𝐴) | ||
This section treats the existing predicate Slot (df-slot 16489) as "evaluation at a class" and for the moment does not introduce new syntax for it. | ||
Theorem | bj-evaleq 34365 | Equality theorem for the Slot construction. This is currently a duplicate of sloteq 16490 but may diverge from it if/when a token Eval is introduced for evaluation in order to separate it from Slot and any of its possible modifications. (Contributed by BJ, 27-Dec-2021.) (Proof modification is discouraged.) |
⊢ (𝐴 = 𝐵 → Slot 𝐴 = Slot 𝐵) | ||
Theorem | bj-evalfun 34366 | The evaluation at a class is a function. (Contributed by BJ, 27-Dec-2021.) |
⊢ Fun Slot 𝐴 | ||
Theorem | bj-evalfn 34367 | The evaluation at a class is a function on the universal class. (General form of slotfn 16503). (Contributed by Mario Carneiro, 22-Sep-2015.) (Revised by BJ, 27-Dec-2021.) |
⊢ Slot 𝐴 Fn V | ||
Theorem | bj-evalval 34368 | Value of the evaluation at a class. (Closed form of strfvnd 16504 and strfvn 16507). (Contributed by NM, 9-Sep-2011.) (Revised by Mario Carneiro, 15-Nov-2014.) (Revised by BJ, 27-Dec-2021.) |
⊢ (𝐹 ∈ 𝑉 → (Slot 𝐴‘𝐹) = (𝐹‘𝐴)) | ||
Theorem | bj-evalid 34369 | The evaluation at a set of the identity function is that set. (General form of ndxarg 16510.) The restriction to a set 𝑉 is necessary since the argument of the function Slot 𝐴 (like that of any function) has to be a set for the evaluation to be meaningful. (Contributed by BJ, 27-Dec-2021.) |
⊢ ((𝑉 ∈ 𝑊 ∧ 𝐴 ∈ 𝑉) → (Slot 𝐴‘( I ↾ 𝑉)) = 𝐴) | ||
Theorem | bj-ndxarg 34370 | Proof of ndxarg 16510 from bj-evalid 34369. (Contributed by BJ, 27-Dec-2021.) (Proof modification is discouraged.) |
⊢ 𝐸 = Slot 𝑁 & ⊢ 𝑁 ∈ ℕ ⇒ ⊢ (𝐸‘ndx) = 𝑁 | ||
Theorem | bj-evalidval 34371 | Closed general form of strndxid 16512. Both sides are equal to (𝐹‘𝐴) by bj-evalid 34369 and bj-evalval 34368 respectively, but bj-evalidval 34371 adds something to bj-evalid 34369 and bj-evalval 34368 in that Slot 𝐴 appears on both sides. (Contributed by BJ, 27-Dec-2021.) |
⊢ ((𝑉 ∈ 𝑊 ∧ 𝐴 ∈ 𝑉 ∧ 𝐹 ∈ 𝑈) → (𝐹‘(Slot 𝐴‘( I ↾ 𝑉))) = (Slot 𝐴‘𝐹)) | ||
Syntax | celwise 34372 | Syntax for elementwise operations. |
class elwise | ||
Definition | df-elwise 34373* | Define the elementwise operation associated with a given operation. For instance, + is the addition of complex numbers (axaddf 10569), so if 𝐴 and 𝐵 are sets of complex numbers, then (𝐴(elwise‘ + )𝐵) is the set of numbers of the form (𝑥 + 𝑦) with 𝑥 ∈ 𝐴 and 𝑦 ∈ 𝐵. The set of odd natural numbers is (({2}(elwise‘ · )ℕ0)(elwise‘ + ){1}), or less formally 2ℕ0 + 1. (Contributed by BJ, 22-Dec-2021.) |
⊢ elwise = (𝑜 ∈ V ↦ (𝑥 ∈ V, 𝑦 ∈ V ↦ {𝑧 ∣ ∃𝑢 ∈ 𝑥 ∃𝑣 ∈ 𝑦 𝑧 = (𝑢𝑜𝑣)})) | ||
Many kinds of structures are given by families of subsets of a given set: Moore collections (df-mre 16859), topologies (df-top 21504), pi-systems, rings of sets, delta-rings, lambda-systems/Dynkin systems, algebras/fields of sets, sigma-algebras/sigma-fields/tribes (df-siga 31370), sigma rings, monotone classes, matroids/independent sets, bornologies, filters. There is a natural notion of structure induced on a subset. It is often given by an elementwise intersection, namely, the family of intersections of sets in the original family with the given subset. In this subsection, we define this notion and prove its main properties. Classical conditions on families of subsets include being nonempty, containing the whole set, containing the empty set, being stable under unions, intersections, subsets, supersets, (relative) complements. Therefore, we prove related properties for the elementwise intersection. We will call (𝑋 ↾t 𝐴) the elementwise intersection on the family 𝑋 by the class 𝐴. REMARK: many theorems are already in set.mm: "MM> SEARCH *rest* / JOIN". | ||
Theorem | bj-rest00 34374 | An elementwise intersection on the empty family is the empty set. TODO: this is 0rest 16705. (Contributed by BJ, 27-Apr-2021.) |
⊢ (∅ ↾t 𝐴) = ∅ | ||
Theorem | bj-restsn 34375 | An elementwise intersection on the singleton on a set is the singleton on the intersection by that set. Generalization of bj-restsn0 34378 and bj-restsnid 34380. (Contributed by BJ, 27-Apr-2021.) |
⊢ ((𝑌 ∈ 𝑉 ∧ 𝐴 ∈ 𝑊) → ({𝑌} ↾t 𝐴) = {(𝑌 ∩ 𝐴)}) | ||
Theorem | bj-restsnss 34376 | Special case of bj-restsn 34375. (Contributed by BJ, 27-Apr-2021.) |
⊢ ((𝑌 ∈ 𝑉 ∧ 𝐴 ⊆ 𝑌) → ({𝑌} ↾t 𝐴) = {𝐴}) | ||
Theorem | bj-restsnss2 34377 | Special case of bj-restsn 34375. (Contributed by BJ, 27-Apr-2021.) |
⊢ ((𝐴 ∈ 𝑉 ∧ 𝑌 ⊆ 𝐴) → ({𝑌} ↾t 𝐴) = {𝑌}) | ||
Theorem | bj-restsn0 34378 | An elementwise intersection on the singleton on the empty set is the singleton on the empty set. Special case of bj-restsn 34375 and bj-restsnss2 34377. TODO: this is restsn 21780. (Contributed by BJ, 27-Apr-2021.) |
⊢ (𝐴 ∈ 𝑉 → ({∅} ↾t 𝐴) = {∅}) | ||
Theorem | bj-restsn10 34379 | Special case of bj-restsn 34375, bj-restsnss 34376, and bj-rest10 34381. (Contributed by BJ, 27-Apr-2021.) |
⊢ (𝑋 ∈ 𝑉 → ({𝑋} ↾t ∅) = {∅}) | ||
Theorem | bj-restsnid 34380 | The elementwise intersection on the singleton on a class by that class is the singleton on that class. Special case of bj-restsn 34375 and bj-restsnss 34376. (Contributed by BJ, 27-Apr-2021.) |
⊢ ({𝐴} ↾t 𝐴) = {𝐴} | ||
Theorem | bj-rest10 34381 | An elementwise intersection on a nonempty family by the empty set is the singleton on the empty set. TODO: this generalizes rest0 21779 and could replace it. (Contributed by BJ, 27-Apr-2021.) |
⊢ (𝑋 ∈ 𝑉 → (𝑋 ≠ ∅ → (𝑋 ↾t ∅) = {∅})) | ||
Theorem | bj-rest10b 34382 | Alternate version of bj-rest10 34381. (Contributed by BJ, 27-Apr-2021.) |
⊢ (𝑋 ∈ (𝑉 ∖ {∅}) → (𝑋 ↾t ∅) = {∅}) | ||
Theorem | bj-restn0 34383 | An elementwise intersection on a nonempty family is nonempty. (Contributed by BJ, 27-Apr-2021.) |
⊢ ((𝑋 ∈ 𝑉 ∧ 𝐴 ∈ 𝑊) → (𝑋 ≠ ∅ → (𝑋 ↾t 𝐴) ≠ ∅)) | ||
Theorem | bj-restn0b 34384 | Alternate version of bj-restn0 34383. (Contributed by BJ, 27-Apr-2021.) |
⊢ ((𝑋 ∈ (𝑉 ∖ {∅}) ∧ 𝐴 ∈ 𝑊) → (𝑋 ↾t 𝐴) ≠ ∅) | ||
Theorem | bj-restpw 34385 | The elementwise intersection on a powerset is the powerset of the intersection. This allows to prove for instance that the topology induced on a subset by the discrete topology is the discrete topology on that subset. See also restdis 21788 (which uses distop 21605 and restopn2 21787). (Contributed by BJ, 27-Apr-2021.) |
⊢ ((𝑌 ∈ 𝑉 ∧ 𝐴 ∈ 𝑊) → (𝒫 𝑌 ↾t 𝐴) = 𝒫 (𝑌 ∩ 𝐴)) | ||
Theorem | bj-rest0 34386 | An elementwise intersection on a family containing the empty set contains the empty set. (Contributed by BJ, 27-Apr-2021.) |
⊢ ((𝑋 ∈ 𝑉 ∧ 𝐴 ∈ 𝑊) → (∅ ∈ 𝑋 → ∅ ∈ (𝑋 ↾t 𝐴))) | ||
Theorem | bj-restb 34387 | An elementwise intersection by a set on a family containing a superset of that set contains that set. (Contributed by BJ, 27-Apr-2021.) |
⊢ (𝑋 ∈ 𝑉 → ((𝐴 ⊆ 𝐵 ∧ 𝐵 ∈ 𝑋) → 𝐴 ∈ (𝑋 ↾t 𝐴))) | ||
Theorem | bj-restv 34388 | An elementwise intersection by a subset on a family containing the whole set contains the whole subset. (Contributed by BJ, 27-Apr-2021.) |
⊢ ((𝐴 ⊆ ∪ 𝑋 ∧ ∪ 𝑋 ∈ 𝑋) → 𝐴 ∈ (𝑋 ↾t 𝐴)) | ||
Theorem | bj-resta 34389 | An elementwise intersection by a set on a family containing that set contains that set. (Contributed by BJ, 27-Apr-2021.) |
⊢ (𝑋 ∈ 𝑉 → (𝐴 ∈ 𝑋 → 𝐴 ∈ (𝑋 ↾t 𝐴))) | ||
Theorem | bj-restuni 34390 | The union of an elementwise intersection by a set is equal to the intersection with that set of the union of the family. See also restuni 21772 and restuni2 21777. (Contributed by BJ, 27-Apr-2021.) |
⊢ ((𝑋 ∈ 𝑉 ∧ 𝐴 ∈ 𝑊) → ∪ (𝑋 ↾t 𝐴) = (∪ 𝑋 ∩ 𝐴)) | ||
Theorem | bj-restuni2 34391 | The union of an elementwise intersection on a family of sets by a subset is equal to that subset. See also restuni 21772 and restuni2 21777. (Contributed by BJ, 27-Apr-2021.) |
⊢ ((𝑋 ∈ 𝑉 ∧ 𝐴 ⊆ ∪ 𝑋) → ∪ (𝑋 ↾t 𝐴) = 𝐴) | ||
Theorem | bj-restreg 34392 | A reformulation of the axiom of regularity using elementwise intersection. (RK: might have to be placed later since theorems in this section are to be moved early (in the section related to the algebra of sets).) (Contributed by BJ, 27-Apr-2021.) |
⊢ ((𝐴 ∈ 𝑉 ∧ 𝐴 ≠ ∅) → ∅ ∈ (𝐴 ↾t 𝐴)) | ||
Theorem | bj-intss 34393 | A nonempty intersection of a family of subsets of a class is included in that class. (Contributed by BJ, 7-Dec-2021.) |
⊢ (𝐴 ⊆ 𝒫 𝑋 → (𝐴 ≠ ∅ → ∩ 𝐴 ⊆ 𝑋)) | ||
Theorem | bj-raldifsn 34394* | All elements in a set satisfy a given property if and only if all but one satisfy that property and that one also does. Typically, this can be used for characterizations that are proved using different methods for a given element and for all others, for instance zero and nonzero numbers, or the empty set and nonempty sets. (Contributed by BJ, 7-Dec-2021.) |
⊢ (𝑥 = 𝐵 → (𝜑 ↔ 𝜓)) ⇒ ⊢ (𝐵 ∈ 𝐴 → (∀𝑥 ∈ 𝐴 𝜑 ↔ (∀𝑥 ∈ (𝐴 ∖ {𝐵})𝜑 ∧ 𝜓))) | ||
Theorem | bj-0int 34395* | If 𝐴 is a collection of subsets of 𝑋, like a Moore collection or a topology, two equivalent ways to say that arbitrary intersections of elements of 𝐴 relative to 𝑋 belong to some class 𝐵: the LHS singles out the empty intersection (the empty intersection relative to 𝑋 is 𝑋 and the intersection of a nonempty family of subsets of 𝑋 is included in 𝑋, so there is no need to intersect it with 𝑋). In typical applications, 𝐵 is 𝐴 itself. (Contributed by BJ, 7-Dec-2021.) |
⊢ (𝐴 ⊆ 𝒫 𝑋 → ((𝑋 ∈ 𝐵 ∧ ∀𝑥 ∈ (𝒫 𝐴 ∖ {∅})∩ 𝑥 ∈ 𝐵) ↔ ∀𝑥 ∈ 𝒫 𝐴(𝑋 ∩ ∩ 𝑥) ∈ 𝐵)) | ||
Theorem | bj-mooreset 34396* |
A Moore collection is a set. Therefore, the class Moore of all
Moore sets defined in df-bj-moore 34398 is actually the class of all Moore
collections. This is also illustrated by the lack of sethood condition
in bj-ismoore 34399.
Note that the closed sets of a topology form a Moore collection, so a topology is a set, and this remark also applies to many other families of sets (namely, as soon as the whole set is required to be a set of the family, then the associated kind of family has no proper classes: that this condition suffices to impose sethood can be seen in this proof, which relies crucially on uniexr 7487). Note: if, in the above predicate, we substitute 𝒫 𝑋 for 𝐴, then the last ∈ 𝒫 𝑋 could be weakened to ⊆ 𝑋, and then the predicate would be obviously satisfied since ⊢ ∪ 𝒫 𝑋 = 𝑋 (unipw 5345) , making 𝒫 𝑋 a Moore collection in this weaker sense, for any class 𝑋, even proper, but the addition of this single case does not add anything interesting. Instead, we have the biconditional bj-discrmoore 34405. (Contributed by BJ, 8-Dec-2021.) |
⊢ (∀𝑥 ∈ 𝒫 𝐴(∪ 𝐴 ∩ ∩ 𝑥) ∈ 𝐴 → 𝐴 ∈ V) | ||
Syntax | cmoore 34397 | Syntax for the class of Moore collections. |
class Moore | ||
Definition | df-bj-moore 34398* |
Define the class of Moore collections. This is indeed the class of all
Moore collections since these all are sets, as proved in bj-mooreset 34396,
and as illustrated by the lack of sethood condition in bj-ismoore 34399.
This is to df-mre 16859 (defining Moore) what df-top 21504 (defining Top) is to df-topon 21521 (defining TopOn). For the sake of consistency, the function defined at df-mre 16859 should be denoted by "MooreOn". Note: df-mre 16859 singles out the empty intersection. This is not necessary. It could be written instead ⊢ Moore = (𝑥 ∈ V ↦ {𝑦 ∈ 𝒫 𝒫 𝑥 ∣ ∀𝑧 ∈ 𝒫 𝑦(𝑥 ∩ ∩ 𝑧) ∈ 𝑦}) and the equivalence of both definitions is proved by bj-0int 34395. There is no added generality in defining a "Moore predicate" for arbitrary classes, since a Moore class satisfying such a predicate is automatically a set (see bj-mooreset 34396). TODO: move to the main section. For many families of sets, one can define both the function associating to each set the set of families of that kind on it (like df-mre 16859 and df-topon 21521) or the class of all families of that kind, independent of a base set (like df-bj-moore 34398 or df-top 21504). In general, the former will be more useful and the extra generality of the latter is not necessary. Moore collections, however, are particular in that they are more ubiquitous and are used in a wide variety of applications (for many families of sets, the family of families of a given kind is often a Moore collection, for instance). Therefore, in the case of Moore families, having both definitions is useful. (Contributed by BJ, 27-Apr-2021.) |
⊢ Moore = {𝑥 ∣ ∀𝑦 ∈ 𝒫 𝑥(∪ 𝑥 ∩ ∩ 𝑦) ∈ 𝑥} | ||
Theorem | bj-ismoore 34399* | Characterization of Moore collections. Note that there is no sethood hypothesis on 𝐴: it is implied by either side (this is obvious for the LHS, and is the content of bj-mooreset 34396 for the RHS). (Contributed by BJ, 9-Dec-2021.) |
⊢ (𝐴 ∈ Moore ↔ ∀𝑥 ∈ 𝒫 𝐴(∪ 𝐴 ∩ ∩ 𝑥) ∈ 𝐴) | ||
Theorem | bj-ismoored0 34400 | Necessary condition to be a Moore collection. (Contributed by BJ, 9-Dec-2021.) |
⊢ (𝐴 ∈ Moore → ∪ 𝐴 ∈ 𝐴) |
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