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Theorem List for Metamath Proof Explorer - 40501-40600   *Has distinct variable group(s)
TypeLabelDescription
Statement

Theoremfrege80 40501* Add additional condition to both clauses of frege79 40500. Proposition 80 of [Frege1879] p. 63. (Contributed by RP, 1-Jul-2020.) (Revised by RP, 5-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑅𝑊    &   𝐴𝐵       ((𝑋𝐴 → (𝑅 hereditary 𝐴 → ∀𝑎(𝑋𝑅𝑎𝑎𝐴))) → (𝑋𝐴 → (𝑅 hereditary 𝐴 → (𝑋(t+‘𝑅)𝑌𝑌𝐴))))

Theoremfrege81 40502 If 𝑋 has a property 𝐴 that is hereditary in the 𝑅 -sequence, and if 𝑌 follows 𝑋 in the 𝑅-sequence, then 𝑌 has property 𝐴. This is a form of induction attributed to Jakob Bernoulli. Proposition 81 of [Frege1879] p. 63. (Contributed by RP, 1-Jul-2020.) (Revised by RP, 5-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑅𝑊    &   𝐴𝐵       (𝑋𝐴 → (𝑅 hereditary 𝐴 → (𝑋(t+‘𝑅)𝑌𝑌𝐴)))

Theoremfrege82 40503 Closed-form deduction based on frege81 40502. Proposition 82 of [Frege1879] p. 64. (Contributed by RP, 1-Jul-2020.) (Revised by RP, 5-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑅𝑊    &   𝐴𝐵       ((𝜑𝑋𝐴) → (𝑅 hereditary 𝐴 → (𝜑 → (𝑋(t+‘𝑅)𝑌𝑌𝐴))))

Theoremfrege83 40504 Apply commuted form of frege81 40502 when the property 𝑅 is hereditary in a disjunction of two properties, only one of which is known to be held by 𝑋. Proposition 83 of [Frege1879] p. 65. Here we introduce the union of classes where Frege has a disjunction of properties which are represented by membership in either of the classes. (Contributed by RP, 1-Jul-2020.) (Revised by RP, 5-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑆    &   𝑌𝑇    &   𝑅𝑈    &   𝐵𝑉    &   𝐶𝑊       (𝑅 hereditary (𝐵𝐶) → (𝑋𝐵 → (𝑋(t+‘𝑅)𝑌𝑌 ∈ (𝐵𝐶))))

Theoremfrege84 40505 Commuted form of frege81 40502. Proposition 84 of [Frege1879] p. 65. (Contributed by RP, 1-Jul-2020.) (Revised by RP, 5-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑅𝑊    &   𝐴𝐵       (𝑅 hereditary 𝐴 → (𝑋𝐴 → (𝑋(t+‘𝑅)𝑌𝑌𝐴)))

Theoremfrege85 40506* Commuted form of frege77 40498. Proposition 85 of [Frege1879] p. 66. (Contributed by RP, 1-Jul-2020.) (Revised by RP, 5-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑅𝑊    &   𝐴𝐵       (𝑋(t+‘𝑅)𝑌 → (∀𝑧(𝑋𝑅𝑧𝑧𝐴) → (𝑅 hereditary 𝐴𝑌𝐴)))

Theoremfrege86 40507* Conclusion about element one past 𝑌 in the 𝑅-sequence. Proposition 86 of [Frege1879] p. 66. (Contributed by RP, 1-Jul-2020.) (Revised by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑅𝑊    &   𝐴𝐵       (((𝑅 hereditary 𝐴𝑌𝐴) → (𝑅 hereditary 𝐴 → (𝑌𝑅𝑍𝑍𝐴))) → (𝑋(t+‘𝑅)𝑌 → (∀𝑤(𝑋𝑅𝑤𝑤𝐴) → (𝑅 hereditary 𝐴 → (𝑌𝑅𝑍𝑍𝐴)))))

Theoremfrege87 40508* If 𝑍 is a result of an application of the procedure 𝑅 to an object 𝑌 that follows 𝑋 in the 𝑅-sequence and if every result of an application of the procedure 𝑅 to 𝑋 has a property 𝐴 that is hereditary in the 𝑅-sequence, then 𝑍 has property 𝐴. Proposition 87 of [Frege1879] p. 66. (Contributed by RP, 1-Jul-2020.) (Revised by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑍𝑊    &   𝑅𝑆    &   𝐴𝐵       (𝑋(t+‘𝑅)𝑌 → (∀𝑤(𝑋𝑅𝑤𝑤𝐴) → (𝑅 hereditary 𝐴 → (𝑌𝑅𝑍𝑍𝐴))))

Theoremfrege88 40509* Commuted form of frege87 40508. Proposition 88 of [Frege1879] p. 67. (Contributed by RP, 1-Jul-2020.) (Revised by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑍𝑊    &   𝑅𝑆    &   𝐴𝐵       (𝑌𝑅𝑍 → (𝑋(t+‘𝑅)𝑌 → (∀𝑤(𝑋𝑅𝑤𝑤𝐴) → (𝑅 hereditary 𝐴𝑍𝐴))))

Theoremfrege89 40510* One direction of dffrege76 40497. Proposition 89 of [Frege1879] p. 68. (Contributed by RP, 1-Jul-2020.) (Revised by RP, 2-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑅𝑊       (∀𝑓(𝑅 hereditary 𝑓 → (∀𝑤(𝑋𝑅𝑤𝑤𝑓) → 𝑌𝑓)) → 𝑋(t+‘𝑅)𝑌)

Theoremfrege90 40511* Add antecedent to frege89 40510. Proposition 90 of [Frege1879] p. 68. (Contributed by RP, 1-Jul-2020.) (Revised by RP, 2-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑅𝑊       ((𝜑 → ∀𝑓(𝑅 hereditary 𝑓 → (∀𝑤(𝑋𝑅𝑤𝑤𝑓) → 𝑌𝑓))) → (𝜑𝑋(t+‘𝑅)𝑌))

Theoremfrege91 40512 Every result of an application of a procedure 𝑅 to an object 𝑋 follows that 𝑋 in the 𝑅-sequence. Proposition 91 of [Frege1879] p. 68. (Contributed by RP, 2-Jul-2020.) (Revised by RP, 5-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑅𝑊       (𝑋𝑅𝑌𝑋(t+‘𝑅)𝑌)

Theoremfrege92 40513 Inference from frege91 40512. Proposition 92 of [Frege1879] p. 69. (Contributed by RP, 2-Jul-2020.) (Revised by RP, 5-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑅𝑊       (𝑋 = 𝑍 → (𝑋𝑅𝑌𝑍(t+‘𝑅)𝑌))

Theoremfrege93 40514* Necessary condition for two elements to be related by the transitive closure. Proposition 93 of [Frege1879] p. 70. (Contributed by RP, 2-Jul-2020.) (Revised by RP, 5-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑅𝑊       (∀𝑓(∀𝑧(𝑋𝑅𝑧𝑧𝑓) → (𝑅 hereditary 𝑓𝑌𝑓)) → 𝑋(t+‘𝑅)𝑌)

Theoremfrege94 40515* Looking one past a pair related by transitive closure of a relation. Proposition 94 of [Frege1879] p. 70. (Contributed by RP, 2-Jul-2020.) (Revised by RP, 5-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑍𝑉    &   𝑅𝑊       ((𝑌𝑅𝑍 → (𝑋(t+‘𝑅)𝑌 → ∀𝑓(∀𝑤(𝑋𝑅𝑤𝑤𝑓) → (𝑅 hereditary 𝑓𝑍𝑓)))) → (𝑌𝑅𝑍 → (𝑋(t+‘𝑅)𝑌𝑋(t+‘𝑅)𝑍)))

Theoremfrege95 40516 Looking one past a pair related by transitive closure of a relation. Proposition 95 of [Frege1879] p. 70. (Contributed by RP, 2-Jul-2020.) (Revised by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑍𝑊    &   𝑅𝐴       (𝑌𝑅𝑍 → (𝑋(t+‘𝑅)𝑌𝑋(t+‘𝑅)𝑍))

Theoremfrege96 40517 Every result of an application of the procedure 𝑅 to an object that follows 𝑋 in the 𝑅-sequence follows 𝑋 in the 𝑅 -sequence. Proposition 96 of [Frege1879] p. 71. (Contributed by RP, 2-Jul-2020.) (Revised by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑍𝑊    &   𝑅𝐴       (𝑋(t+‘𝑅)𝑌 → (𝑌𝑅𝑍𝑋(t+‘𝑅)𝑍))

Theoremfrege97 40518 The property of following 𝑋 in the 𝑅-sequence is hereditary in the 𝑅-sequence. Proposition 97 of [Frege1879] p. 71.

Here we introduce the image of a singleton under a relation as class which stands for the property of following 𝑋 in the 𝑅 -sequence. (Contributed by RP, 2-Jul-2020.) (Revised by RP, 7-Jul-2020.) (Proof modification is discouraged.)

𝑋𝑈    &   𝑅𝑊       𝑅 hereditary ((t+‘𝑅) “ {𝑋})

Theoremfrege98 40519 If 𝑌 follows 𝑋 and 𝑍 follows 𝑌 in the 𝑅-sequence then 𝑍 follows 𝑋 in the 𝑅-sequence because the transitive closure of a relation has the transitive property. Proposition 98 of [Frege1879] p. 71. (Contributed by RP, 2-Jul-2020.) (Revised by RP, 6-Jul-2020.) (Proof modification is discouraged.)
𝑋𝐴    &   𝑌𝐵    &   𝑍𝐶    &   𝑅𝐷       (𝑋(t+‘𝑅)𝑌 → (𝑌(t+‘𝑅)𝑍𝑋(t+‘𝑅)𝑍))

20.31.3.10  _Begriffsschrift_ Chapter III Member of sequence

𝑝((t+‘𝑅) ∪ I )𝑐 means 𝑐 is a member of the 𝑅 -sequence begining with 𝑝 and 𝑝 is a member of the 𝑅 -sequence ending with 𝑐.

dffrege99 40520 through frege114 40535 develop this.

This will be shown to be related to the transitive-reflexive closure of relation 𝑅. But more work needs to be done on transitive closure of relations before this is ready for Metamath.

Theoremdffrege99 40520 If 𝑍 is identical with 𝑋 or follows 𝑋 in the 𝑅 -sequence, then we say : "𝑍 belongs to the 𝑅-sequence beginning with 𝑋 " or "𝑋 belongs to the 𝑅-sequence ending with 𝑍". Definition 99 of [Frege1879] p. 71. (Contributed by RP, 2-Jul-2020.)
𝑍𝑈       ((¬ 𝑋(t+‘𝑅)𝑍𝑍 = 𝑋) ↔ 𝑋((t+‘𝑅) ∪ I )𝑍)

Theoremfrege100 40521 One direction of dffrege99 40520. Proposition 100 of [Frege1879] p. 72. (Contributed by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑍𝑈       (𝑋((t+‘𝑅) ∪ I )𝑍 → (¬ 𝑋(t+‘𝑅)𝑍𝑍 = 𝑋))

Theoremfrege101 40522 Lemma for frege102 40523. Proposition 101 of [Frege1879] p. 72. (Contributed by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑍𝑈       ((𝑍 = 𝑋 → (𝑍𝑅𝑉𝑋(t+‘𝑅)𝑉)) → ((𝑋(t+‘𝑅)𝑍 → (𝑍𝑅𝑉𝑋(t+‘𝑅)𝑉)) → (𝑋((t+‘𝑅) ∪ I )𝑍 → (𝑍𝑅𝑉𝑋(t+‘𝑅)𝑉))))

Theoremfrege102 40523 If 𝑍 belongs to the 𝑅-sequence beginning with 𝑋, then every result of an application of the procedure 𝑅 to 𝑍 follows 𝑋 in the 𝑅-sequence. Proposition 102 of [Frege1879] p. 72. (Contributed by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑋𝐴    &   𝑍𝐵    &   𝑉𝐶    &   𝑅𝐷       (𝑋((t+‘𝑅) ∪ I )𝑍 → (𝑍𝑅𝑉𝑋(t+‘𝑅)𝑉))

Theoremfrege103 40524 Proposition 103 of [Frege1879] p. 73. (Contributed by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑍𝑉       ((𝑍 = 𝑋𝑋 = 𝑍) → (𝑋((t+‘𝑅) ∪ I )𝑍 → (¬ 𝑋(t+‘𝑅)𝑍𝑋 = 𝑍)))

Theoremfrege104 40525 Proposition 104 of [Frege1879] p. 73.

Note: in the Bauer-Meenfelberg translation published in van Heijenoort's collection From Frege to Goedel, this proof has the minor clause and result swapped. (Contributed by RP, 7-Jul-2020.) (Proof modification is discouraged.)

𝑍𝑉       (𝑋((t+‘𝑅) ∪ I )𝑍 → (¬ 𝑋(t+‘𝑅)𝑍𝑋 = 𝑍))

Theoremfrege105 40526 Proposition 105 of [Frege1879] p. 73. (Contributed by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑍𝑉       ((¬ 𝑋(t+‘𝑅)𝑍𝑍 = 𝑋) → 𝑋((t+‘𝑅) ∪ I )𝑍)

Theoremfrege106 40527 Whatever follows 𝑋 in the 𝑅-sequence belongs to the 𝑅 -sequence beginning with 𝑋. Proposition 106 of [Frege1879] p. 73. (Contributed by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑍𝑉       (𝑋(t+‘𝑅)𝑍𝑋((t+‘𝑅) ∪ I )𝑍)

Theoremfrege107 40528 Proposition 107 of [Frege1879] p. 74. (Contributed by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑉𝐴       ((𝑍((t+‘𝑅) ∪ I )𝑌 → (𝑌𝑅𝑉𝑍(t+‘𝑅)𝑉)) → (𝑍((t+‘𝑅) ∪ I )𝑌 → (𝑌𝑅𝑉𝑍((t+‘𝑅) ∪ I )𝑉)))

Theoremfrege108 40529 If 𝑌 belongs to the 𝑅-sequence beginning with 𝑍, then every result of an application of the procedure 𝑅 to 𝑌 belongs to the 𝑅-sequence beginning with 𝑍. Proposition 108 of [Frege1879] p. 74. (Contributed by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑍𝐴    &   𝑌𝐵    &   𝑉𝐶    &   𝑅𝐷       (𝑍((t+‘𝑅) ∪ I )𝑌 → (𝑌𝑅𝑉𝑍((t+‘𝑅) ∪ I )𝑉))

Theoremfrege109 40530 The property of belonging to the 𝑅-sequence beginning with 𝑋 is hereditary in the 𝑅-sequence. Proposition 109 of [Frege1879] p. 74. (Contributed by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑅𝑉       𝑅 hereditary (((t+‘𝑅) ∪ I ) “ {𝑋})

Theoremfrege110 40531* Proposition 110 of [Frege1879] p. 75. (Contributed by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑋𝐴    &   𝑌𝐵    &   𝑀𝐶    &   𝑅𝐷       (∀𝑎(𝑌𝑅𝑎𝑋((t+‘𝑅) ∪ I )𝑎) → (𝑌(t+‘𝑅)𝑀𝑋((t+‘𝑅) ∪ I )𝑀))

Theoremfrege111 40532 If 𝑌 belongs to the 𝑅-sequence beginning with 𝑍, then every result of an application of the procedure 𝑅 to 𝑌 belongs to the 𝑅-sequence beginning with 𝑍 or precedes 𝑍 in the 𝑅-sequence. Proposition 111 of [Frege1879] p. 75. (Contributed by RP, 7-Jul-2020.) (Revised by RP, 8-Jul-2020.) (Proof modification is discouraged.)
𝑍𝐴    &   𝑌𝐵    &   𝑉𝐶    &   𝑅𝐷       (𝑍((t+‘𝑅) ∪ I )𝑌 → (𝑌𝑅𝑉 → (¬ 𝑉(t+‘𝑅)𝑍𝑍((t+‘𝑅) ∪ I )𝑉)))

Theoremfrege112 40533 Identity implies belonging to the 𝑅-sequence beginning with self. Proposition 112 of [Frege1879] p. 76. (Contributed by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑍𝑉       (𝑍 = 𝑋𝑋((t+‘𝑅) ∪ I )𝑍)

Theoremfrege113 40534 Proposition 113 of [Frege1879] p. 76. (Contributed by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑍𝑉       ((𝑍((t+‘𝑅) ∪ I )𝑋 → (¬ 𝑍(t+‘𝑅)𝑋𝑍 = 𝑋)) → (𝑍((t+‘𝑅) ∪ I )𝑋 → (¬ 𝑍(t+‘𝑅)𝑋𝑋((t+‘𝑅) ∪ I )𝑍)))

Theoremfrege114 40535 If 𝑋 belongs to the 𝑅-sequence beginning with 𝑍, then 𝑍 belongs to the 𝑅-sequence beginning with 𝑋 or 𝑋 follows 𝑍 in the 𝑅-sequence. Proposition 114 of [Frege1879] p. 76. (Contributed by RP, 7-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑍𝑉       (𝑍((t+‘𝑅) ∪ I )𝑋 → (¬ 𝑍(t+‘𝑅)𝑋𝑋((t+‘𝑅) ∪ I )𝑍))

20.31.3.11  _Begriffsschrift_ Chapter III Single-valued procedures

Fun 𝑅 means the relationship content of procedure 𝑅 is single-valued. The double converse allows us to simply apply this syntax in place of Frege's even though the original never explicitly limited discussion of propositional statements which vary on two variables to relations.

dffrege115 40536 through frege133 40554 develop this and how functions relate to transitive and transitive-reflexive closures.

Theoremdffrege115 40536* If from the circumstance that 𝑐 is a result of an application of the procedure 𝑅 to 𝑏, whatever 𝑏 may be, it can be inferred that every result of an application of the procedure 𝑅 to 𝑏 is the same as 𝑐, then we say : "The procedure 𝑅 is single-valued". Definition 115 of [Frege1879] p. 77. (Contributed by RP, 7-Jul-2020.)
(∀𝑐𝑏(𝑏𝑅𝑐 → ∀𝑎(𝑏𝑅𝑎𝑎 = 𝑐)) ↔ Fun 𝑅)

Theoremfrege116 40537* One direction of dffrege115 40536. Proposition 116 of [Frege1879] p. 77. (Contributed by RP, 8-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈       (Fun 𝑅 → ∀𝑏(𝑏𝑅𝑋 → ∀𝑎(𝑏𝑅𝑎𝑎 = 𝑋)))

Theoremfrege117 40538* Lemma for frege118 40539. Proposition 117 of [Frege1879] p. 78. (Contributed by RP, 8-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈       ((∀𝑏(𝑏𝑅𝑋 → ∀𝑎(𝑏𝑅𝑎𝑎 = 𝑋)) → (𝑌𝑅𝑋 → ∀𝑎(𝑌𝑅𝑎𝑎 = 𝑋))) → (Fun 𝑅 → (𝑌𝑅𝑋 → ∀𝑎(𝑌𝑅𝑎𝑎 = 𝑋))))

Theoremfrege118 40539* Simplified application of one direction of dffrege115 40536. Proposition 118 of [Frege1879] p. 78. (Contributed by RP, 8-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉       (Fun 𝑅 → (𝑌𝑅𝑋 → ∀𝑎(𝑌𝑅𝑎𝑎 = 𝑋)))

Theoremfrege119 40540* Lemma for frege120 40541. Proposition 119 of [Frege1879] p. 78. (Contributed by RP, 8-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉       ((∀𝑎(𝑌𝑅𝑎𝑎 = 𝑋) → (𝑌𝑅𝐴𝐴 = 𝑋)) → (Fun 𝑅 → (𝑌𝑅𝑋 → (𝑌𝑅𝐴𝐴 = 𝑋))))

Theoremfrege120 40541 Simplified application of one direction of dffrege115 40536. Proposition 120 of [Frege1879] p. 78. (Contributed by RP, 8-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝐴𝑊       (Fun 𝑅 → (𝑌𝑅𝑋 → (𝑌𝑅𝐴𝐴 = 𝑋)))

Theoremfrege121 40542 Lemma for frege122 40543. Proposition 121 of [Frege1879] p. 79. (Contributed by RP, 8-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝐴𝑊       ((𝐴 = 𝑋𝑋((t+‘𝑅) ∪ I )𝐴) → (Fun 𝑅 → (𝑌𝑅𝑋 → (𝑌𝑅𝐴𝑋((t+‘𝑅) ∪ I )𝐴))))

Theoremfrege122 40543 If 𝑋 is a result of an application of the single-valued procedure 𝑅 to 𝑌, then every result of an application of the procedure 𝑅 to 𝑌 belongs to the 𝑅-sequence beginning with 𝑋. Proposition 122 of [Frege1879] p. 79. (Contributed by RP, 8-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝐴𝑊       (Fun 𝑅 → (𝑌𝑅𝑋 → (𝑌𝑅𝐴𝑋((t+‘𝑅) ∪ I )𝐴)))

Theoremfrege123 40544* Lemma for frege124 40545. Proposition 123 of [Frege1879] p. 79. (Contributed by RP, 8-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉       ((∀𝑎(𝑌𝑅𝑎𝑋((t+‘𝑅) ∪ I )𝑎) → (𝑌(t+‘𝑅)𝑀𝑋((t+‘𝑅) ∪ I )𝑀)) → (Fun 𝑅 → (𝑌𝑅𝑋 → (𝑌(t+‘𝑅)𝑀𝑋((t+‘𝑅) ∪ I )𝑀))))

Theoremfrege124 40545 If 𝑋 is a result of an application of the single-valued procedure 𝑅 to 𝑌 and if 𝑀 follows 𝑌 in the 𝑅-sequence, then 𝑀 belongs to the 𝑅-sequence beginning with 𝑋. Proposition 124 of [Frege1879] p. 80. (Contributed by RP, 8-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑀𝑊    &   𝑅𝑆       (Fun 𝑅 → (𝑌𝑅𝑋 → (𝑌(t+‘𝑅)𝑀𝑋((t+‘𝑅) ∪ I )𝑀)))

Theoremfrege125 40546 Lemma for frege126 40547. Proposition 125 of [Frege1879] p. 81. (Contributed by RP, 9-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑀𝑊    &   𝑅𝑆       ((𝑋((t+‘𝑅) ∪ I )𝑀 → (¬ 𝑋(t+‘𝑅)𝑀𝑀((t+‘𝑅) ∪ I )𝑋)) → (Fun 𝑅 → (𝑌𝑅𝑋 → (𝑌(t+‘𝑅)𝑀 → (¬ 𝑋(t+‘𝑅)𝑀𝑀((t+‘𝑅) ∪ I )𝑋)))))

Theoremfrege126 40547 If 𝑀 follows 𝑌 in the 𝑅-sequence and if the procedure 𝑅 is single-valued, then every result of an application of the procedure 𝑅 to 𝑌 belongs to the 𝑅-sequence beginning with 𝑀 or precedes 𝑀 in the 𝑅-sequence. Proposition 126 of [Frege1879] p. 81. (Contributed by RP, 9-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑀𝑊    &   𝑅𝑆       (Fun 𝑅 → (𝑌𝑅𝑋 → (𝑌(t+‘𝑅)𝑀 → (¬ 𝑋(t+‘𝑅)𝑀𝑀((t+‘𝑅) ∪ I )𝑋))))

Theoremfrege127 40548 Communte antecedents of frege126 40547. Proposition 127 of [Frege1879] p. 82. (Contributed by RP, 9-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑀𝑊    &   𝑅𝑆       (Fun 𝑅 → (𝑌(t+‘𝑅)𝑀 → (𝑌𝑅𝑋 → (¬ 𝑋(t+‘𝑅)𝑀𝑀((t+‘𝑅) ∪ I )𝑋))))

Theoremfrege128 40549 Lemma for frege129 40550. Proposition 128 of [Frege1879] p. 83. (Contributed by RP, 9-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑀𝑊    &   𝑅𝑆       ((𝑀((t+‘𝑅) ∪ I )𝑌 → (𝑌𝑅𝑋 → (¬ 𝑋(t+‘𝑅)𝑀𝑀((t+‘𝑅) ∪ I )𝑋))) → (Fun 𝑅 → ((¬ 𝑌(t+‘𝑅)𝑀𝑀((t+‘𝑅) ∪ I )𝑌) → (𝑌𝑅𝑋 → (¬ 𝑋(t+‘𝑅)𝑀𝑀((t+‘𝑅) ∪ I )𝑋)))))

Theoremfrege129 40550 If the procedure 𝑅 is single-valued and 𝑌 belongs to the 𝑅 -sequence begining with 𝑀 or precedes 𝑀 in the 𝑅-sequence, then every result of an application of the procedure 𝑅 to 𝑌 belongs to the 𝑅-sequence begining with 𝑀 or precedes 𝑀 in the 𝑅-sequence. Proposition 129 of [Frege1879] p. 83. (Contributed by RP, 9-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑀𝑊    &   𝑅𝑆       (Fun 𝑅 → ((¬ 𝑌(t+‘𝑅)𝑀𝑀((t+‘𝑅) ∪ I )𝑌) → (𝑌𝑅𝑋 → (¬ 𝑋(t+‘𝑅)𝑀𝑀((t+‘𝑅) ∪ I )𝑋))))

Theoremfrege130 40551* Lemma for frege131 40552. Proposition 130 of [Frege1879] p. 84. (Contributed by RP, 9-Jul-2020.) (Proof modification is discouraged.)
𝑀𝑈    &   𝑅𝑉       ((∀𝑏((¬ 𝑏(t+‘𝑅)𝑀𝑀((t+‘𝑅) ∪ I )𝑏) → ∀𝑎(𝑏𝑅𝑎 → (¬ 𝑎(t+‘𝑅)𝑀𝑀((t+‘𝑅) ∪ I )𝑎))) → 𝑅 hereditary (((t+‘𝑅) “ {𝑀}) ∪ (((t+‘𝑅) ∪ I ) “ {𝑀}))) → (Fun 𝑅𝑅 hereditary (((t+‘𝑅) “ {𝑀}) ∪ (((t+‘𝑅) ∪ I ) “ {𝑀}))))

Theoremfrege131 40552 If the procedure 𝑅 is single-valued, then the property of belonging to the 𝑅-sequence begining with 𝑀 or preceeding 𝑀 in the 𝑅-sequence is hereditary in the 𝑅-sequence. Proposition 131 of [Frege1879] p. 85. (Contributed by RP, 9-Jul-2020.) (Proof modification is discouraged.)
𝑀𝑈    &   𝑅𝑉       (Fun 𝑅𝑅 hereditary (((t+‘𝑅) “ {𝑀}) ∪ (((t+‘𝑅) ∪ I ) “ {𝑀})))

Theoremfrege132 40553 Lemma for frege133 40554. Proposition 132 of [Frege1879] p. 86. (Contributed by RP, 9-Jul-2020.) (Proof modification is discouraged.)
𝑀𝑈    &   𝑅𝑉       ((𝑅 hereditary (((t+‘𝑅) “ {𝑀}) ∪ (((t+‘𝑅) ∪ I ) “ {𝑀})) → (𝑋(t+‘𝑅)𝑀 → (𝑋(t+‘𝑅)𝑌 → (¬ 𝑌(t+‘𝑅)𝑀𝑀((t+‘𝑅) ∪ I )𝑌)))) → (Fun 𝑅 → (𝑋(t+‘𝑅)𝑀 → (𝑋(t+‘𝑅)𝑌 → (¬ 𝑌(t+‘𝑅)𝑀𝑀((t+‘𝑅) ∪ I )𝑌)))))

Theoremfrege133 40554 If the procedure 𝑅 is single-valued and if 𝑀 and 𝑌 follow 𝑋 in the 𝑅-sequence, then 𝑌 belongs to the 𝑅-sequence beginning with 𝑀 or precedes 𝑀 in the 𝑅-sequence. Proposition 133 of [Frege1879] p. 86. (Contributed by RP, 9-Jul-2020.) (Proof modification is discouraged.)
𝑋𝑈    &   𝑌𝑉    &   𝑀𝑊    &   𝑅𝑆       (Fun 𝑅 → (𝑋(t+‘𝑅)𝑀 → (𝑋(t+‘𝑅)𝑌 → (¬ 𝑌(t+‘𝑅)𝑀𝑀((t+‘𝑅) ∪ I )𝑌))))

20.31.4  Exploring Topology via Seifert and Threlfall

See Seifert and Threlfall: A Textbook Of Topology (1980) which is an English translation of Lehrbuch der Topologie (1934).

20.31.4.1  Equinumerosity of sets of relations and maps

Because ((2om 𝐵) ↑m 𝐴) ≈ (2om (𝐴 × 𝐵)) ≈ ((2om 𝐴) ↑m 𝐵) is an instance of the law of exponents: ((𝐶m 𝐵) ↑m 𝐴) ≈ (𝐶m (𝐴 × 𝐵)) ≈ ((𝐶m 𝐴) ↑m 𝐵) we are led to see that (𝒫 𝐵m 𝐴) ≈ 𝒫 (𝐴 × 𝐵) ≈ (𝒫 𝐴m 𝐵) is true for any two sets, 𝐴 and 𝐵, and thus there exist one-to-one onto relations between each of these three sets of relations.

Theoremenrelmap 40555 The set of all possible relations between two sets is equinumerous to the set of all mappings from one set to the powerset of the other. See rfovf1od 40564 for a demonstration of a natural one-to-one onto mapping. (Contributed by RP, 27-Apr-2021.)
((𝐴𝑉𝐵𝑊) → 𝒫 (𝐴 × 𝐵) ≈ (𝒫 𝐵m 𝐴))

Theoremenrelmapr 40556 The set of all possible relations between two sets is equinumerous to the set of all mappings from one set to the powerset of the other. (Contributed by RP, 27-Apr-2021.)
((𝐴𝑉𝐵𝑊) → 𝒫 (𝐴 × 𝐵) ≈ (𝒫 𝐴m 𝐵))

Theoremenmappw 40557 The set of all mappings from one set to the powerset of the other is equinumerous to the set of all mappings from the second set to the powerset of the first. (Contributed by RP, 27-Apr-2021.)
((𝐴𝑉𝐵𝑊) → (𝒫 𝐵m 𝐴) ≈ (𝒫 𝐴m 𝐵))

Theoremenmappwid 40558 The set of all mappings from the powerset to the powerset is equinumerous to the set of all mappings from the set to the powerset of the powerset. (Contributed by RP, 27-Apr-2021.)
(𝐴𝑉 → (𝒫 𝐴m 𝒫 𝐴) ≈ (𝒫 𝒫 𝐴m 𝐴))

Theoremrfovd 40559* Value of the operator, (𝐴𝑂𝐵), which maps between relations and functions for relations between base sets, 𝐴 and 𝐵. (Contributed by RP, 25-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑟 ∈ 𝒫 (𝑎 × 𝑏) ↦ (𝑥𝑎 ↦ {𝑦𝑏𝑥𝑟𝑦})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)       (𝜑 → (𝐴𝑂𝐵) = (𝑟 ∈ 𝒫 (𝐴 × 𝐵) ↦ (𝑥𝐴 ↦ {𝑦𝐵𝑥𝑟𝑦})))

Theoremrfovfvd 40560* Value of the operator, (𝐴𝑂𝐵), which maps between relations and functions for relations between base sets, 𝐴 and 𝐵, and relation 𝑅. (Contributed by RP, 25-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑟 ∈ 𝒫 (𝑎 × 𝑏) ↦ (𝑥𝑎 ↦ {𝑦𝑏𝑥𝑟𝑦})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)    &   (𝜑𝑅 ∈ 𝒫 (𝐴 × 𝐵))    &   𝐹 = (𝐴𝑂𝐵)       (𝜑 → (𝐹𝑅) = (𝑥𝐴 ↦ {𝑦𝐵𝑥𝑅𝑦}))

Theoremrfovfvfvd 40561* Value of the operator, (𝐴𝑂𝐵), which maps between relations and functions for relations between base sets, 𝐴 and 𝐵, relation 𝑅, and left element 𝑋. (Contributed by RP, 25-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑟 ∈ 𝒫 (𝑎 × 𝑏) ↦ (𝑥𝑎 ↦ {𝑦𝑏𝑥𝑟𝑦})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)    &   (𝜑𝑅 ∈ 𝒫 (𝐴 × 𝐵))    &   𝐹 = (𝐴𝑂𝐵)    &   (𝜑𝑋𝐴)    &   𝐺 = (𝐹𝑅)       (𝜑 → (𝐺𝑋) = {𝑦𝐵𝑋𝑅𝑦})

Theoremrfovcnvf1od 40562* Properties of the operator, (𝐴𝑂𝐵), which maps between relations and functions for relations between base sets, 𝐴 and 𝐵. (Contributed by RP, 27-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑟 ∈ 𝒫 (𝑎 × 𝑏) ↦ (𝑥𝑎 ↦ {𝑦𝑏𝑥𝑟𝑦})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)    &   𝐹 = (𝐴𝑂𝐵)       (𝜑 → (𝐹:𝒫 (𝐴 × 𝐵)–1-1-onto→(𝒫 𝐵m 𝐴) ∧ 𝐹 = (𝑓 ∈ (𝒫 𝐵m 𝐴) ↦ {⟨𝑥, 𝑦⟩ ∣ (𝑥𝐴𝑦 ∈ (𝑓𝑥))})))

Theoremrfovcnvd 40563* Value of the converse of the operator, (𝐴𝑂𝐵), which maps between relations and functions for relations between base sets, 𝐴 and 𝐵. (Contributed by RP, 27-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑟 ∈ 𝒫 (𝑎 × 𝑏) ↦ (𝑥𝑎 ↦ {𝑦𝑏𝑥𝑟𝑦})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)    &   𝐹 = (𝐴𝑂𝐵)       (𝜑𝐹 = (𝑓 ∈ (𝒫 𝐵m 𝐴) ↦ {⟨𝑥, 𝑦⟩ ∣ (𝑥𝐴𝑦 ∈ (𝑓𝑥))}))

Theoremrfovf1od 40564* The value of the operator, (𝐴𝑂𝐵), which maps between relations and functions for relations between base sets, 𝐴 and 𝐵, is a bijection. (Contributed by RP, 27-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑟 ∈ 𝒫 (𝑎 × 𝑏) ↦ (𝑥𝑎 ↦ {𝑦𝑏𝑥𝑟𝑦})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)    &   𝐹 = (𝐴𝑂𝐵)       (𝜑𝐹:𝒫 (𝐴 × 𝐵)–1-1-onto→(𝒫 𝐵m 𝐴))

Theoremrfovcnvfvd 40565* Value of the converse of the operator, (𝐴𝑂𝐵), which maps between relations and functions for relations between base sets, 𝐴 and 𝐵, evaluated at function 𝐺. (Contributed by RP, 27-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑟 ∈ 𝒫 (𝑎 × 𝑏) ↦ (𝑥𝑎 ↦ {𝑦𝑏𝑥𝑟𝑦})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)    &   𝐹 = (𝐴𝑂𝐵)    &   (𝜑𝐺 ∈ (𝒫 𝐵m 𝐴))       (𝜑 → (𝐹𝐺) = {⟨𝑥, 𝑦⟩ ∣ (𝑥𝐴𝑦 ∈ (𝐺𝑥))})

Theoremfsovd 40566* Value of the operator, (𝐴𝑂𝐵), which maps between maps from one base set to subsets of the second to maps from the second base set to subsets of the first for base sets, 𝐴 and 𝐵. (Contributed by RP, 25-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝑎) ↦ (𝑦𝑏 ↦ {𝑥𝑎𝑦 ∈ (𝑓𝑥)})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)       (𝜑 → (𝐴𝑂𝐵) = (𝑓 ∈ (𝒫 𝐵m 𝐴) ↦ (𝑦𝐵 ↦ {𝑥𝐴𝑦 ∈ (𝑓𝑥)})))

Theoremfsovrfovd 40567* The operator which gives a 1-to-1 a mapping to a subset and a reverse mapping from elements can be composed from the operator which gives a 1-to-1 mapping between relations and functions to subsets and the converse operator. (Contributed by RP, 15-May-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝑎) ↦ (𝑦𝑏 ↦ {𝑥𝑎𝑦 ∈ (𝑓𝑥)})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)    &   𝑅 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑟 ∈ 𝒫 (𝑎 × 𝑏) ↦ (𝑢𝑎 ↦ {𝑣𝑏𝑢𝑟𝑣})))    &   𝐶 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑠 ∈ 𝒫 (𝑎 × 𝑏) ↦ 𝑠))       (𝜑 → (𝐴𝑂𝐵) = ((𝐵𝑅𝐴) ∘ ((𝐴𝐶𝐵) ∘ (𝐴𝑅𝐵))))

Theoremfsovfvd 40568* Value of the operator, (𝐴𝑂𝐵), which maps between maps from one base set to subsets of the second to maps from the second base set to subsets of the first for base sets, 𝐴 and 𝐵, when applied to function 𝐹. (Contributed by RP, 25-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝑎) ↦ (𝑦𝑏 ↦ {𝑥𝑎𝑦 ∈ (𝑓𝑥)})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)    &   𝐺 = (𝐴𝑂𝐵)    &   (𝜑𝐹 ∈ (𝒫 𝐵m 𝐴))       (𝜑 → (𝐺𝐹) = (𝑦𝐵 ↦ {𝑥𝐴𝑦 ∈ (𝐹𝑥)}))

Theoremfsovfvfvd 40569* Value of the operator, (𝐴𝑂𝐵), which maps between maps from one base set to subsets of the second to maps from the second base set to subsets of the first for base sets, 𝐴 and 𝐵, when applied to function 𝐹 and element 𝑌. (Contributed by RP, 25-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝑎) ↦ (𝑦𝑏 ↦ {𝑥𝑎𝑦 ∈ (𝑓𝑥)})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)    &   𝐺 = (𝐴𝑂𝐵)    &   (𝜑𝐹 ∈ (𝒫 𝐵m 𝐴))    &   𝐻 = (𝐺𝐹)    &   (𝜑𝑌𝐵)       (𝜑 → (𝐻𝑌) = {𝑥𝐴𝑌 ∈ (𝐹𝑥)})

Theoremfsovfd 40570* The operator, (𝐴𝑂𝐵), which maps between maps from one base set to subsets of the second to maps from the second base set to subsets of the first for base sets, 𝐴 and 𝐵, gives a function between two sets of functions. (Contributed by RP, 27-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝑎) ↦ (𝑦𝑏 ↦ {𝑥𝑎𝑦 ∈ (𝑓𝑥)})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)    &   𝐺 = (𝐴𝑂𝐵)       (𝜑𝐺:(𝒫 𝐵m 𝐴)⟶(𝒫 𝐴m 𝐵))

Theoremfsovcnvlem 40571* The 𝑂 operator, which maps between maps from one base set to subsets of the second to maps from the second base set to subsets of the first for base sets, gives a family of functions that include their own inverse. (Contributed by RP, 27-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝑎) ↦ (𝑦𝑏 ↦ {𝑥𝑎𝑦 ∈ (𝑓𝑥)})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)    &   𝐺 = (𝐴𝑂𝐵)    &   𝐻 = (𝐵𝑂𝐴)       (𝜑 → (𝐻𝐺) = ( I ↾ (𝒫 𝐵m 𝐴)))

Theoremfsovcnvd 40572* The value of the converse (𝐴𝑂𝐵) is (𝐵𝑂𝐴), where 𝑂 is the operator which maps between maps from one base set to subsets of the second to maps from the second base set to subsets of the first for base sets, gives a family of functions that include their own inverse. (Contributed by RP, 27-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝑎) ↦ (𝑦𝑏 ↦ {𝑥𝑎𝑦 ∈ (𝑓𝑥)})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)    &   𝐺 = (𝐴𝑂𝐵)    &   𝐻 = (𝐵𝑂𝐴)       (𝜑𝐺 = 𝐻)

Theoremfsovcnvfvd 40573* The value of the converse of (𝐴𝑂𝐵), where 𝑂 is the operator which maps between maps from one base set to subsets of the second to maps from the second base set to subsets of the first for base sets, evaluated at function 𝐹. (Contributed by RP, 27-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝑎) ↦ (𝑦𝑏 ↦ {𝑥𝑎𝑦 ∈ (𝑓𝑥)})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)    &   𝐺 = (𝐴𝑂𝐵)    &   (𝜑𝐹 ∈ (𝒫 𝐴m 𝐵))       (𝜑 → (𝐺𝐹) = (𝑦𝐴 ↦ {𝑥𝐵𝑦 ∈ (𝐹𝑥)}))

Theoremfsovf1od 40574* The value of (𝐴𝑂𝐵) is a bijection, where 𝑂 is the operator which maps between maps from one base set to subsets of the second to maps from the second base set to subsets of the first for base sets. (Contributed by RP, 27-Apr-2021.)
𝑂 = (𝑎 ∈ V, 𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝑎) ↦ (𝑦𝑏 ↦ {𝑥𝑎𝑦 ∈ (𝑓𝑥)})))    &   (𝜑𝐴𝑉)    &   (𝜑𝐵𝑊)    &   𝐺 = (𝐴𝑂𝐵)       (𝜑𝐺:(𝒫 𝐵m 𝐴)–1-1-onto→(𝒫 𝐴m 𝐵))

Theoremdssmapfvd 40575* Value of the duality operator for self-mappings of subsets of a base set, 𝐵. (Contributed by RP, 19-Apr-2021.)
𝑂 = (𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝒫 𝑏) ↦ (𝑠 ∈ 𝒫 𝑏 ↦ (𝑏 ∖ (𝑓‘(𝑏𝑠))))))    &   𝐷 = (𝑂𝐵)    &   (𝜑𝐵𝑉)       (𝜑𝐷 = (𝑓 ∈ (𝒫 𝐵m 𝒫 𝐵) ↦ (𝑠 ∈ 𝒫 𝐵 ↦ (𝐵 ∖ (𝑓‘(𝐵𝑠))))))

Theoremdssmapfv2d 40576* Value of the duality operator for self-mappings of subsets of a base set, 𝐵 when applied to function 𝐹. (Contributed by RP, 19-Apr-2021.)
𝑂 = (𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝒫 𝑏) ↦ (𝑠 ∈ 𝒫 𝑏 ↦ (𝑏 ∖ (𝑓‘(𝑏𝑠))))))    &   𝐷 = (𝑂𝐵)    &   (𝜑𝐵𝑉)    &   (𝜑𝐹 ∈ (𝒫 𝐵m 𝒫 𝐵))    &   𝐺 = (𝐷𝐹)       (𝜑𝐺 = (𝑠 ∈ 𝒫 𝐵 ↦ (𝐵 ∖ (𝐹‘(𝐵𝑠)))))

Theoremdssmapfv3d 40577* Value of the duality operator for self-mappings of subsets of a base set, 𝐵 when applied to function 𝐹 and subset 𝑆. (Contributed by RP, 19-Apr-2021.)
𝑂 = (𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝒫 𝑏) ↦ (𝑠 ∈ 𝒫 𝑏 ↦ (𝑏 ∖ (𝑓‘(𝑏𝑠))))))    &   𝐷 = (𝑂𝐵)    &   (𝜑𝐵𝑉)    &   (𝜑𝐹 ∈ (𝒫 𝐵m 𝒫 𝐵))    &   𝐺 = (𝐷𝐹)    &   (𝜑𝑆 ∈ 𝒫 𝐵)    &   𝑇 = (𝐺𝑆)       (𝜑𝑇 = (𝐵 ∖ (𝐹‘(𝐵𝑆))))

Theoremdssmapnvod 40578* For any base set 𝐵 the duality operator for self-mappings of subsets of that base set is its own inverse, an involution. (Contributed by RP, 20-Apr-2021.)
𝑂 = (𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝒫 𝑏) ↦ (𝑠 ∈ 𝒫 𝑏 ↦ (𝑏 ∖ (𝑓‘(𝑏𝑠))))))    &   𝐷 = (𝑂𝐵)    &   (𝜑𝐵𝑉)       (𝜑𝐷 = 𝐷)

Theoremdssmapf1od 40579* For any base set 𝐵 the duality operator for self-mappings of subsets of that base set is one-to-one and onto. (Contributed by RP, 21-Apr-2021.)
𝑂 = (𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝒫 𝑏) ↦ (𝑠 ∈ 𝒫 𝑏 ↦ (𝑏 ∖ (𝑓‘(𝑏𝑠))))))    &   𝐷 = (𝑂𝐵)    &   (𝜑𝐵𝑉)       (𝜑𝐷:(𝒫 𝐵m 𝒫 𝐵)–1-1-onto→(𝒫 𝐵m 𝒫 𝐵))

Theoremdssmap2d 40580* For any base set 𝐵 the duality operator for self-mappings of subsets of that base set when composed with itself is the restricted identity operator. (Contributed by RP, 21-Apr-2021.)
𝑂 = (𝑏 ∈ V ↦ (𝑓 ∈ (𝒫 𝑏m 𝒫 𝑏) ↦ (𝑠 ∈ 𝒫 𝑏 ↦ (𝑏 ∖ (𝑓‘(𝑏𝑠))))))    &   𝐷 = (𝑂𝐵)    &   (𝜑𝐵𝑉)       (𝜑 → (𝐷𝐷) = ( I ↾ (𝒫 𝐵m 𝒫 𝐵)))

20.31.4.2  Generic Pseudoclosure Spaces, Pseudointerior Spaces, and Pseudoneighborhoods

For any base set, 𝐵, an arbitrary mapping of subsets to subsets can be called a pseudoclosure (pseudointerior) function, 𝐾, with its dual of a pseudointerior (pseudoclosure), 𝐼, related by the involution in dssmapfvd 40575. As 𝐾 gains properties of the closure (interior) function of a topology on 𝐵, so does its dual gain corresponding properties of the interior (closure) function of that topology.

As (𝒫 𝐵m 𝒫 𝐵) ≈ (𝒫 𝒫 𝐵m 𝐵) there is also a natural isomorphism which maps from 𝐼 to 𝑁 (and likewise for 𝐾 and 𝑀, introduced below) which identically gains the properties of the neighborhood function of a topology (modified and restricted to operate on single points). A function dual to 𝑁, which Stadler and Stadler refer to as a convergent function, is represented by 𝑀 in this section.

Based on this and the early treatment of topology in Seifert and Threlfall, it seems reasonable to define a pseudotopology as defined in terms of its base set and one of these functions with theorems treating the equivalence of the other definitions and adding topological structure if enough properties hold true.

 Neighborhoods Interior Closure Convergents Theorems Functions 𝑁 ∈ (𝒫 𝒫 𝐵 ↑m 𝐵) 𝐼 ∈ (𝒫 𝐵 ↑m 𝒫 𝐵) 𝐾 ∈ (𝒫 𝐵 ↑m 𝒫 𝐵) 𝑀 ∈ (𝒫 𝒫 𝐵 ↑m 𝐵) Correspondences (assuming (𝑋 ∈ 𝐵 ∧ 𝑆 ∈ 𝒫 𝐵)) 𝑆 ∈ (𝑁‘𝑋) ↔ 𝑋 ∈ (𝐼‘𝑆) ↔ ¬ 𝑋 ∈ (𝐾‘(𝐵 ∖ 𝑆)) ↔ ¬ (𝐵 ∖ 𝑆) ∈ (𝑀‘𝑋) ntrclselnel1 40619, ntrneiel 40643, neicvgel1 40681 ¬ (𝐵 ∖ 𝑆) ∈ (𝑁‘𝑋) ↔ ¬ 𝑋 ∈ (𝐼‘(𝐵 ∖ 𝑆)) ↔ 𝑋 ∈ (𝐾‘𝑆) ↔ 𝑆 ∈ (𝑀‘𝑋) (𝑁‘𝑋) = {𝑠 ∈ 𝒫 𝐵 ∣ 𝑋 ∈ (𝐼‘𝑠)} = {𝑠 ∈ 𝒫 𝐵 ∣ ¬ 𝑋 ∈ (𝐾‘(𝐵 ∖ 𝑠))} = {𝑠 ∈ 𝒫 𝐵 ∣ ¬ (𝐵 ∖ 𝑠) ∈ (𝑀‘𝑋)} ntrneifv3 40644, clsneifv3 40672, neicvgfv 40683 {𝑥 ∈ 𝐵 ∣ 𝑆 ∈ (𝑁‘𝑥)} = (𝐼‘𝑆) = (𝐵 ∖ (𝐾‘(𝐵 ∖ 𝑆))) = {𝑥 ∈ 𝐵 ∣ ¬ (𝐵 ∖ 𝑆) ∈ (𝑀‘𝑥)} ntrneifv4 40647, ntrclsfv 40621, clsneifv4 40673 {𝑥 ∈ 𝐵 ∣ ¬ (𝐵 ∖ 𝑆) ∈ (𝑁‘𝑥)} = (𝐵 ∖ (𝐼‘(𝐵 ∖ 𝑆))) = (𝐾‘𝑆) = {𝑥 ∈ 𝐵 ∣ 𝑆 ∈ (𝑀‘𝑥)} clsneifv4 40673, ntrclsfv 40621, ntrneifv4 40647 {𝑠 ∈ 𝒫 𝐵 ∣ ¬ (𝐵 ∖ 𝑠) ∈ (𝑁‘𝑋)} = {𝑠 ∈ 𝒫 𝐵 ∣ ¬ 𝑋 ∈ (𝐼‘(𝐵 ∖ 𝑠))} = {𝑠 ∈ 𝒫 𝐵 ∣ 𝑋 ∈ (𝐾‘𝑠)} = (𝑀‘𝑋) neicvgfv 40683, clsneifv3 40672, ntrneifv3 40644

We have the following table of equivalences to axioms largely established by Kuratowski. In the formulas in this table, to reduce the width of the columns, if any of the variables 𝑥, 𝑠, or 𝑡 are used, then they are implicitly universally quantified and 𝑥 (respectively 𝑠 and 𝑡) ranges over 𝐵 (respectively 𝒫 𝐵 and 𝒫 𝐵).

 Neighborhoods Interior Closure Convergents Equivalence Theorems Assuming a prefix of: ∀𝑥 ∈ 𝐵∀𝑠 ∈ 𝒫 𝐵∀𝑡 ∈ 𝒫 𝐵 (𝑁‘𝑥) ≠ ∅ ∃𝑢 ∈ 𝒫 𝐵𝑥 ∈ (𝐼‘𝑢) ∃𝑢 ∈ 𝒫 𝐵¬ 𝑥 ∈ (𝐾‘𝑢) (𝑀‘𝑥) ≠ 𝒫 𝐵 ntrclsneine0 40627, ntrneineine0 40649, ntrneineine1 40650 (𝑁‘𝑥) ≠ 𝒫 𝐵 ∃𝑢 ∈ 𝒫 𝐵¬ 𝑥 ∈ (𝐼‘𝑢) ∃𝑢 ∈ 𝒫 𝐵𝑥 ∈ (𝐾‘𝑢) (𝑀‘𝑥) ≠ ∅ ntrclsneine0 40627, ntrneineine0 40649, ntrneineine1 40650 𝐵 ∈ (𝑁‘𝑥) (𝐼‘𝐵) = 𝐵 (𝐾‘∅) = ∅ ¬ ∅ ∈ (𝑀‘𝑥) ntrclscls00 40628, ntrneicls00 40651, ntrneicls11 40652 ¬ ∅ ∈ (𝑁‘𝑥) (𝐼‘∅) = ∅ (𝐾‘𝐵) = 𝐵 𝐵 ∈ (𝑀‘𝑥) ntrclscls00 40628, ntrneicls00 40651, ntrneicls11 40652 ((𝑠 ∈ (𝑁‘𝑥) ∧ 𝑠 ⊆ 𝑡) → 𝑡 ∈ (𝑁‘𝑥)) (𝑠 ⊆ 𝑡 → (𝐼‘𝑠) ⊆ (𝐼‘𝑡)) — or — ((𝐼‘𝑠) ∪ (𝐼‘𝑡)) ⊆ (𝐼‘(𝑠 ∪ 𝑡)) — or — (𝐼‘(𝑠 ∩ 𝑡)) ⊆ ((𝐼‘𝑠) ∩ (𝐼‘𝑡)) (𝑠 ⊆ 𝑡 → (𝐾‘𝑠) ⊆ (𝐾‘𝑡)) — or — ((𝐾‘𝑠) ∪ (𝐾‘𝑡)) ⊆ (𝐾‘(𝑠 ∪ 𝑡)) — or — (𝐾‘(𝑠 ∩ 𝑡)) ⊆ ((𝐾‘𝑠) ∩ (𝐾‘𝑡)) ((𝑠 ∈ (𝑀‘𝑥) ∧ 𝑠 ⊆ 𝑡) → 𝑡 ∈ (𝑀‘𝑥)) isotone1 40610, isotone2 40611, ntrclsiso 40629, ntrneiiso 40653 (𝑠 ∈ (𝑁‘𝑥) → 𝑥 ∈ 𝑠) (𝐼‘𝑠) ⊆ 𝑠 𝑠 ⊆ (𝐾‘𝑠) (𝑥 ∈ 𝑠 → 𝑠 ∈ (𝑀‘𝑥)) ntrclsk2 40630, ntrneik2 40654, ntrneix2 40655 ((𝑠 ∈ (𝑁‘𝑥) ∧ 𝑡 ∈ (𝑁‘𝑥)) → (𝑠 ∩ 𝑡) ≠ ∅) ((𝑠 ∩ 𝑡) = ∅ → ((𝐼‘𝑠) ∩ (𝐼‘𝑡)) = ∅) ((𝑠 ∪ 𝑡) = 𝐵 → ((𝐾‘𝑠) ∪ (𝐾‘𝑡)) = 𝐵) ((𝑠 ∪ 𝑡) = 𝐵 → (𝑠 ∈ (𝑀‘𝑥) ∨ 𝑡 ∈ (𝑀‘𝑥))) ntrclskb 40631, ntrneikb 40656, ntrneixb 40657 ((𝑠 ∈ (𝑁‘𝑥) ∧ 𝑡 ∈ (𝑁‘𝑥)) → (𝑠 ∩ 𝑡) ∈ (𝑁‘𝑥)) ((𝐼‘𝑠) ∩ (𝐼‘𝑡)) ⊆ (𝐼‘(𝑠 ∩ 𝑡)) (𝐾‘(𝑠 ∪ 𝑡)) ⊆ ((𝐾‘𝑠) ∪ (𝐾‘𝑡)) ((𝑠 ∪ 𝑡) ∈ (𝑀‘𝑥) → (𝑠 ∈ (𝑀‘𝑥) ∨ 𝑡 ∈ (𝑀‘𝑥))) ntrclsk3 40632, ntrneik3 40658, ntrneix3 40659 ((𝑠 ∩ 𝑡) ∈ (𝑁‘𝑥) ↔ (𝑠 ∈ (𝑁‘𝑥) ∧ 𝑡 ∈ (𝑁‘𝑥))) (𝐼‘(𝑠 ∩ 𝑡)) = ((𝐼‘𝑠) ∩ (𝐼‘𝑡)) (𝐾‘(𝑠 ∪ 𝑡)) = ((𝐾‘𝑠) ∪ (𝐾‘𝑡)) ((𝑠 ∪ 𝑡) ∈ (𝑀‘𝑥) ↔ (𝑠 ∈ (𝑀‘𝑥) ∨ 𝑡 ∈ (𝑀‘𝑥))) ntrclsk13 40633, ntrneik13 40660, ntrneix13 40661 (𝑠 ∈ (𝑁‘𝑥) ↔ ∃𝑢 ∈ (𝑁‘𝑥)∀𝑦 ∈ 𝐵 (𝑦 ∈ 𝑢 ↔ 𝑠 ∈ (𝑁‘𝑦))) (𝐼‘(𝐼‘𝑠)) = (𝐼‘𝑠) (𝐾‘(𝐾‘𝑠)) = (𝐾‘𝑠) (𝑠 ∈ (𝑀‘𝑥) ↔ ∃𝑢 ∈ (𝑀‘𝑥)∀𝑦 ∈ 𝐵 (𝑦 ∈ 𝑢 ↔ 𝑠 ∈ (𝑀‘𝑦))) ntrclsk4 40634, ntrneik4 40663

Using these properties as axiomic constraints on the functions, certain collections of them give rise to named spaces.

Space Foundational Axioms Derived Axioms Theorems
Csázár Generalized Neighborhood Space K2 KA', KA, KB ntrk2imkb 40599, ntrkbimka 40600, neik0imk0p 40598
Min Strong Generalized Neighborhood Space K2, K3 KA', KA, KB ntrk2imkb 40599, ntrkbimka 40600, neik0imk0p 40598
Gniłka Extended Topology K0', K1 K0 neik0pk1imk0 40609
Brissaud Space K0, K2 K0', KA', KA, KB neik0imk0p 40598, ntrk2imkb 40599, ntrkbimka 40600
Neighborhood Space K0', K1, K2 K0, KA', KA, KB neik0pk1imk0 40609, ntrk2imkb 40599, ntrkbimka 40600, neik0imk0p 40598
Davey and Priestley Intersection Structure K1, K4
Moore Closure Space K1, K2, K4 KA', KA, KB ntrk2imkb 40599, ntrkbimka 40600, neik0imk0p 40598
Convex Closure Space K0', K1, K2, K4 K0, KA', KA, KB neik0pk1imk0 40609, ntrk2imkb 40599, ntrkbimka 40600, neik0imk0p 40598
Smyth Neighborhood Space K0', K13 K0, K1, K3 neik0pk1imk0 40609, ntrk1k3eqk13 40612
Čech Closure Space
Pretopological Space
K0', K2, K13 K0, K1, KA', KA, KB, K3 neik0pk1imk0 40609, ntrk2imkb 40599, ntrkbimka 40600, neik0imk0p 40598, ntrk1k3eqk13 40612
Topological Space K0', K2, K13, K4 K0, K1, KA', KA, KB, K3 neik0pk1imk0 40609, ntrk2imkb 40599, ntrkbimka 40600, neik0imk0p 40598, ntrk1k3eqk13 40612
Alexandroff Space K0', K2, K5 K0, K1, KA', KA, KB, K3, K13 neik0pk1imk0 40609, ntrk2imkb 40599, ntrkbimka 40600, neik0imk0p 40598, ntrk1k3eqk13 40612, TBD
Alexandroff Topological Space K0', K2, K4, K5 K0, K1, KA', KA, KB, K3, K13 neik0pk1imk0 40609, ntrk2imkb 40599, ntrkbimka 40600, neik0imk0p 40598, ntrk1k3eqk13 40612, TBD

Theoremsscon34b 40581 Relative complementation reverses inclusion of subclasses. Relativized version of complss 4109. (Contributed by RP, 3-Jun-2021.)
((𝐴𝐶𝐵𝐶) → (𝐴𝐵 ↔ (𝐶𝐵) ⊆ (𝐶𝐴)))

Theoremrcompleq 40582 Two subclasses are equal if and only if their relative complements are equal. Relativized version of compleq 4110. (Contributed by RP, 10-Jun-2021.)
((𝐴𝐶𝐵𝐶) → (𝐴 = 𝐵 ↔ (𝐶𝐴) = (𝐶𝐵)))

Theoremor3or 40583 Decompose disjunction into three cases. (Contributed by RP, 5-Jul-2021.)
((𝜑𝜓) ↔ ((𝜑𝜓) ∨ (𝜑 ∧ ¬ 𝜓) ∨ (¬ 𝜑𝜓)))

Theoremandi3or 40584 Distribute over triple disjunction. (Contributed by RP, 5-Jul-2021.)
((𝜑 ∧ (𝜓𝜒𝜃)) ↔ ((𝜑𝜓) ∨ (𝜑𝜒) ∨ (𝜑𝜃)))

Theoremuneqsn 40585 If a union of classes is equal to a singleton then at least one class is equal to the singleton while the other may be equal to the empty set. (Contributed by RP, 5-Jul-2021.)
((𝐴𝐵) = {𝐶} ↔ ((𝐴 = {𝐶} ∧ 𝐵 = {𝐶}) ∨ (𝐴 = {𝐶} ∧ 𝐵 = ∅) ∨ (𝐴 = ∅ ∧ 𝐵 = {𝐶})))

Theoremdf3o2 40586 Ordinal 3 is the unordered triple containing ordinals 0, 1, and 2. (Contributed by RP, 8-Jul-2021.)
3o = {∅, 1o, 2o}

Theoremdf3o3 40587 Ordinal 3, fully expanded. (Contributed by RP, 8-Jul-2021.)
3o = {∅, {∅}, {∅, {∅}}}

Theorembrfvimex 40588 If a binary relation holds and the relation is the value of a function, then the argument to that function is a set. (Contributed by RP, 22-May-2021.)
(𝜑𝐴𝑅𝐵)    &   (𝜑𝑅 = (𝐹𝐶))       (𝜑𝐶 ∈ V)

Theorembrovmptimex 40589* If a binary relation holds and the relation is the value of a binary operation built with maps-to, then the arguments to that operation are sets. (Contributed by RP, 22-May-2021.)
𝐹 = (𝑥𝐸, 𝑦𝐺𝐻)    &   (𝜑𝐴𝑅𝐵)    &   (𝜑𝑅 = (𝐶𝐹𝐷))       (𝜑 → (𝐶 ∈ V ∧ 𝐷 ∈ V))

Theorembrovmptimex1 40590* If a binary relation holds and the relation is the value of a binary operation built with maps-to, then the arguments to that operation are sets. (Contributed by RP, 22-May-2021.)
𝐹 = (𝑥𝐸, 𝑦𝐺𝐻)    &   (𝜑𝐴𝑅𝐵)    &   (𝜑𝑅 = (𝐶𝐹𝐷))       (𝜑𝐶 ∈ V)

Theorembrovmptimex2 40591* If a binary relation holds and the relation is the value of a binary operation built with maps-to, then the arguments to that operation are sets. (Contributed by RP, 22-May-2021.)
𝐹 = (𝑥𝐸, 𝑦𝐺𝐻)    &   (𝜑𝐴𝑅𝐵)    &   (𝜑𝑅 = (𝐶𝐹𝐷))       (𝜑𝐷 ∈ V)

Theorembrcoffn 40592 Conditions allowing the decomposition of a binary relation. (Contributed by RP, 7-Jun-2021.)
(𝜑𝐶 Fn 𝑌)    &   (𝜑𝐷:𝑋𝑌)    &   (𝜑𝐴(𝐶𝐷)𝐵)       (𝜑 → (𝐴𝐷(𝐷𝐴) ∧ (𝐷𝐴)𝐶𝐵))

Theorembrcofffn 40593 Conditions allowing the decomposition of a binary relation. (Contributed by RP, 8-Jun-2021.)
(𝜑𝐶 Fn 𝑍)    &   (𝜑𝐷:𝑌𝑍)    &   (𝜑𝐸:𝑋𝑌)    &   (𝜑𝐴(𝐶 ∘ (𝐷𝐸))𝐵)       (𝜑 → (𝐴𝐸(𝐸𝐴) ∧ (𝐸𝐴)𝐷(𝐷‘(𝐸𝐴)) ∧ (𝐷‘(𝐸𝐴))𝐶𝐵))

Theorembrco2f1o 40594 Conditions allowing the decomposition of a binary relation. (Contributed by RP, 8-Jun-2021.)
(𝜑𝐶:𝑌1-1-onto𝑍)    &   (𝜑𝐷:𝑋1-1-onto𝑌)    &   (𝜑𝐴(𝐶𝐷)𝐵)       (𝜑 → ((𝐶𝐵)𝐶𝐵𝐴𝐷(𝐶𝐵)))

Theorembrco3f1o 40595 Conditions allowing the decomposition of a binary relation. (Contributed by RP, 8-Jun-2021.)
(𝜑𝐶:𝑌1-1-onto𝑍)    &   (𝜑𝐷:𝑋1-1-onto𝑌)    &   (𝜑𝐸:𝑊1-1-onto𝑋)    &   (𝜑𝐴(𝐶 ∘ (𝐷𝐸))𝐵)       (𝜑 → ((𝐶𝐵)𝐶𝐵 ∧ (𝐷‘(𝐶𝐵))𝐷(𝐶𝐵) ∧ 𝐴𝐸(𝐷‘(𝐶𝐵))))

Theoremntrclsbex 40596 If (pseudo-)interior and (pseudo-)closure functions are related by the duality operator then the base set exists. (Contributed by RP, 21-May-2021.)
𝐷 = (𝑂𝐵)    &   (𝜑𝐼𝐷𝐾)       (𝜑𝐵 ∈ V)

Theoremntrclsrcomplex 40597 The relative complement of the class 𝑆 exists as a subset of the base set. (Contributed by RP, 25-Jun-2021.)
𝐷 = (𝑂𝐵)    &   (𝜑𝐼𝐷𝐾)       (𝜑 → (𝐵𝑆) ∈ 𝒫 𝐵)

Theoremneik0imk0p 40598 Kuratowski's K0 axiom implies K0'. Neighborhood version. Also a proof the dual KA axiom implies KA' when considering the convergents. (Contributed by RP, 28-Jun-2021.)
(∀𝑥𝐵 𝐵 ∈ (𝑁𝑥) → ∀𝑥𝐵 (𝑁𝑥) ≠ ∅)

Theoremntrk2imkb 40599* If an interior function is contracting, the interiors of disjoint sets are disjoint. Kuratowski's K2 axiom implies KB. Interior version. (Contributed by RP, 9-Jun-2021.)
(∀𝑠 ∈ 𝒫 𝐵(𝐼𝑠) ⊆ 𝑠 → ∀𝑠 ∈ 𝒫 𝐵𝑡 ∈ 𝒫 𝐵((𝑠𝑡) = ∅ → ((𝐼𝑠) ∩ (𝐼𝑡)) = ∅))

Theoremntrkbimka 40600* If the interiors of disjoint sets are disjoint, then the interior of the empty set is the empty set. (Contributed by RP, 14-Jun-2021.)
(∀𝑠 ∈ 𝒫 𝐵𝑡 ∈ 𝒫 𝐵((𝑠𝑡) = ∅ → ((𝐼𝑠) ∩ (𝐼𝑡)) = ∅) → (𝐼‘∅) = ∅)

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