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Theorem List for Intuitionistic Logic Explorer - 6801-6900   *Has distinct variable group(s)
TypeLabelDescription
Statement

Theoremf1finf1o 6801 Any injection from one finite set to another of equal size must be a bijection. (Contributed by Jeff Madsen, 5-Jun-2010.)

Theoremen1eqsn 6802 A set with one element is a singleton. (Contributed by FL, 18-Aug-2008.)

Theoremen1eqsnbi 6803 A set containing an element has exactly one element iff it is a singleton. (Contributed by FL, 13-Feb-2010.) (Revised by AV, 25-Jan-2020.)

Theoremsnexxph 6804* A case where the antecedent of snexg 4076 is not needed. The class is from dcextest 4463. (Contributed by Mario Carneiro and Jim Kingdon, 4-Jul-2022.)

Theorempreimaf1ofi 6805 The preimage of a finite set under a one-to-one, onto function is finite. (Contributed by Jim Kingdon, 24-Sep-2022.)

Theoremfidcenumlemim 6806* Lemma for fidcenum 6810. Forward direction. (Contributed by Jim Kingdon, 19-Oct-2022.)
DECID

Theoremfidcenumlemrks 6807* Lemma for fidcenum 6810. Induction step for fidcenumlemrk 6808. (Contributed by Jim Kingdon, 20-Oct-2022.)
DECID

Theoremfidcenumlemrk 6808* Lemma for fidcenum 6810. (Contributed by Jim Kingdon, 20-Oct-2022.)
DECID

Theoremfidcenumlemr 6809* Lemma for fidcenum 6810. Reverse direction (put into deduction form). (Contributed by Jim Kingdon, 19-Oct-2022.)
DECID

Theoremfidcenum 6810* A set is finite if and only if it has decidable equality and is finitely enumerable. Proposition 8.1.11 of [AczelRathjen], p. 72. The definition of "finitely enumerable" as is Definition 8.1.4 of [AczelRathjen], p. 71. (Contributed by Jim Kingdon, 19-Oct-2022.)
DECID

2.6.31  Schroeder-Bernstein Theorem

Theoremsbthlem1 6811* Lemma for isbth 6821. (Contributed by NM, 22-Mar-1998.)

Theoremsbthlem2 6812* Lemma for isbth 6821. (Contributed by NM, 22-Mar-1998.)

Theoremsbthlemi3 6813* Lemma for isbth 6821. (Contributed by NM, 22-Mar-1998.)
EXMID

Theoremsbthlemi4 6814* Lemma for isbth 6821. (Contributed by NM, 27-Mar-1998.)
EXMID

Theoremsbthlemi5 6815* Lemma for isbth 6821. (Contributed by NM, 22-Mar-1998.)
EXMID

Theoremsbthlemi6 6816* Lemma for isbth 6821. (Contributed by NM, 27-Mar-1998.)
EXMID

Theoremsbthlem7 6817* Lemma for isbth 6821. (Contributed by NM, 27-Mar-1998.)

Theoremsbthlemi8 6818* Lemma for isbth 6821. (Contributed by NM, 27-Mar-1998.)
EXMID

Theoremsbthlemi9 6819* Lemma for isbth 6821. (Contributed by NM, 28-Mar-1998.)
EXMID

Theoremsbthlemi10 6820* Lemma for isbth 6821. (Contributed by NM, 28-Mar-1998.)
EXMID

Theoremisbth 6821 Schroeder-Bernstein Theorem. Theorem 18 of [Suppes] p. 95. This theorem states that if set is smaller (has lower cardinality) than and vice-versa, then and are equinumerous (have the same cardinality). The interesting thing is that this can be proved without invoking the Axiom of Choice, as we do here, but the proof as you can see is quite difficult. (The theorem can be proved more easily if we allow AC.) The main proof consists of lemmas sbthlem1 6811 through sbthlemi10 6820; this final piece mainly changes bound variables to eliminate the hypotheses of sbthlemi10 6820. We follow closely the proof in Suppes, which you should consult to understand our proof at a higher level. Note that Suppes' proof, which is credited to J. M. Whitaker, does not require the Axiom of Infinity. The proof does require the law of the excluded middle which cannot be avoided as shown at exmidsbthr 13052. (Contributed by NM, 8-Jun-1998.)
EXMID

2.6.32  Finite intersections

Syntaxcfi 6822 Extend class notation with the function whose value is the class of finite intersections of the elements of a given set.

Definitiondf-fi 6823* Function whose value is the class of finite intersections of the elements of the argument. Note that the empty intersection being the universal class, hence a proper class, it cannot be an element of that class. Therefore, the function value is the class of nonempty finite intersections of elements of the argument (see elfi2 6826). (Contributed by FL, 27-Apr-2008.)

Theoremfival 6824* The set of all the finite intersections of the elements of . (Contributed by FL, 27-Apr-2008.) (Revised by Mario Carneiro, 24-Nov-2013.)

Theoremelfi 6825* Specific properties of an element of . (Contributed by FL, 27-Apr-2008.) (Revised by Mario Carneiro, 24-Nov-2013.)

Theoremelfi2 6826* The empty intersection need not be considered in the set of finite intersections. (Contributed by Mario Carneiro, 21-Mar-2015.)

Theoremelfir 6827 Sufficient condition for an element of . (Contributed by Mario Carneiro, 24-Nov-2013.)

Theoremssfii 6828 Any element of a set is the intersection of a finite subset of . (Contributed by FL, 27-Apr-2008.) (Proof shortened by Mario Carneiro, 21-Mar-2015.)

Theoremfi0 6829 The set of finite intersections of the empty set. (Contributed by Mario Carneiro, 30-Aug-2015.)

Theoremfieq0 6830 A set is empty iff the class of all the finite intersections of that set is empty. (Contributed by FL, 27-Apr-2008.) (Revised by Mario Carneiro, 24-Nov-2013.)

Theoremfiss 6831 Subset relationship for function . (Contributed by Jeff Hankins, 7-Oct-2009.) (Revised by Mario Carneiro, 24-Nov-2013.)

Theoremfiuni 6832 The union of the finite intersections of a set is simply the union of the set itself. (Contributed by Jeff Hankins, 5-Sep-2009.) (Revised by Mario Carneiro, 24-Nov-2013.)

Theoremfipwssg 6833 If a set is a family of subsets of some base set, then so is its finite intersection. (Contributed by Stefan O'Rear, 2-Aug-2015.)

Theoremfifo 6834* Describe a surjection from nonempty finite sets to finite intersections. (Contributed by Mario Carneiro, 18-May-2015.)

2.6.33  Supremum and infimum

Syntaxcsup 6835 Extend class notation to include supremum of class . Here is ordinarily a relation that strictly orders class . For example, could be 'less than' and could be the set of real numbers.

Syntaxcinf 6836 Extend class notation to include infimum of class . Here is ordinarily a relation that strictly orders class . For example, could be 'less than' and could be the set of real numbers.
inf

Definitiondf-sup 6837* Define the supremum of class . It is meaningful when is a relation that strictly orders and when the supremum exists. (Contributed by NM, 22-May-1999.)

Definitiondf-inf 6838 Define the infimum of class . It is meaningful when is a relation that strictly orders and when the infimum exists. For example, could be 'less than', could be the set of real numbers, and could be the set of all positive reals; in this case the infimum is 0. The infimum is defined as the supremum using the converse ordering relation. In the given example, 0 is the supremum of all reals (greatest real number) for which all positive reals are greater. (Contributed by AV, 2-Sep-2020.)
inf

Theoremsupeq1 6839 Equality theorem for supremum. (Contributed by NM, 22-May-1999.)

Theoremsupeq1d 6840 Equality deduction for supremum. (Contributed by Paul Chapman, 22-Jun-2011.)

Theoremsupeq1i 6841 Equality inference for supremum. (Contributed by Paul Chapman, 22-Jun-2011.)

Theoremsupeq2 6842 Equality theorem for supremum. (Contributed by Jeff Madsen, 2-Sep-2009.)

Theoremsupeq3 6843 Equality theorem for supremum. (Contributed by Scott Fenton, 13-Jun-2018.)

Theoremsupeq123d 6844 Equality deduction for supremum. (Contributed by Stefan O'Rear, 20-Jan-2015.)

Theoremnfsup 6845 Hypothesis builder for supremum. (Contributed by Mario Carneiro, 20-Mar-2014.)

Theoremsupmoti 6846* Any class has at most one supremum in (where is interpreted as 'less than'). The hypothesis is satisfied by real numbers (see lttri3 7808) or other orders which correspond to tight apartnesses. (Contributed by Jim Kingdon, 23-Nov-2021.)

Theoremsupeuti 6847* A supremum is unique. Similar to Theorem I.26 of [Apostol] p. 24 (but for suprema in general). (Contributed by Jim Kingdon, 23-Nov-2021.)

Theoremsupval2ti 6848* Alternate expression for the supremum. (Contributed by Jim Kingdon, 23-Nov-2021.)

Theoremeqsupti 6849* Sufficient condition for an element to be equal to the supremum. (Contributed by Jim Kingdon, 23-Nov-2021.)

Theoremeqsuptid 6850* Sufficient condition for an element to be equal to the supremum. (Contributed by Jim Kingdon, 24-Nov-2021.)

Theoremsupclti 6851* A supremum belongs to its base class (closure law). See also supubti 6852 and suplubti 6853. (Contributed by Jim Kingdon, 24-Nov-2021.)

Theoremsupubti 6852* A supremum is an upper bound. See also supclti 6851 and suplubti 6853.

This proof demonstrates how to expand an iota-based definition (df-iota 5056) using riotacl2 5709.

(Contributed by Jim Kingdon, 24-Nov-2021.)

Theoremsuplubti 6853* A supremum is the least upper bound. See also supclti 6851 and supubti 6852. (Contributed by Jim Kingdon, 24-Nov-2021.)

Theoremsuplub2ti 6854* Bidirectional form of suplubti 6853. (Contributed by Jim Kingdon, 17-Jan-2022.)

Theoremsupelti 6855* Supremum membership in a set. (Contributed by Jim Kingdon, 16-Jan-2022.)

Theoremsup00 6856 The supremum under an empty base set is always the empty set. (Contributed by AV, 4-Sep-2020.)

Theoremsupmaxti 6857* The greatest element of a set is its supremum. Note that the converse is not true; the supremum might not be an element of the set considered. (Contributed by Jim Kingdon, 24-Nov-2021.)

Theoremsupsnti 6858* The supremum of a singleton. (Contributed by Jim Kingdon, 26-Nov-2021.)

Theoremisotilem 6859* Lemma for isoti 6860. (Contributed by Jim Kingdon, 26-Nov-2021.)

Theoremisoti 6860* An isomorphism preserves tightness. (Contributed by Jim Kingdon, 26-Nov-2021.)

Theoremsupisolem 6861* Lemma for supisoti 6863. (Contributed by Mario Carneiro, 24-Dec-2016.)

Theoremsupisoex 6862* Lemma for supisoti 6863. (Contributed by Mario Carneiro, 24-Dec-2016.)

Theoremsupisoti 6863* Image of a supremum under an isomorphism. (Contributed by Jim Kingdon, 26-Nov-2021.)

Theoreminfeq1 6864 Equality theorem for infimum. (Contributed by AV, 2-Sep-2020.)
inf inf

Theoreminfeq1d 6865 Equality deduction for infimum. (Contributed by AV, 2-Sep-2020.)
inf inf

Theoreminfeq1i 6866 Equality inference for infimum. (Contributed by AV, 2-Sep-2020.)
inf inf

Theoreminfeq2 6867 Equality theorem for infimum. (Contributed by AV, 2-Sep-2020.)
inf inf

Theoreminfeq3 6868 Equality theorem for infimum. (Contributed by AV, 2-Sep-2020.)
inf inf

Theoreminfeq123d 6869 Equality deduction for infimum. (Contributed by AV, 2-Sep-2020.)
inf inf

Theoremnfinf 6870 Hypothesis builder for infimum. (Contributed by AV, 2-Sep-2020.)
inf

Theoremcnvinfex 6871* Two ways of expressing existence of an infimum (one in terms of converse). (Contributed by Jim Kingdon, 17-Dec-2021.)

Theoremcnvti 6872* If a relation satisfies a condition corresponding to tightness of an apartness generated by an order, so does its converse. (Contributed by Jim Kingdon, 17-Dec-2021.)

Theoremeqinfti 6873* Sufficient condition for an element to be equal to the infimum. (Contributed by Jim Kingdon, 16-Dec-2021.)
inf

Theoremeqinftid 6874* Sufficient condition for an element to be equal to the infimum. (Contributed by Jim Kingdon, 16-Dec-2021.)
inf

Theoreminfvalti 6875* Alternate expression for the infimum. (Contributed by Jim Kingdon, 17-Dec-2021.)
inf

Theoreminfclti 6876* An infimum belongs to its base class (closure law). See also inflbti 6877 and infglbti 6878. (Contributed by Jim Kingdon, 17-Dec-2021.)
inf

Theoreminflbti 6877* An infimum is a lower bound. See also infclti 6876 and infglbti 6878. (Contributed by Jim Kingdon, 18-Dec-2021.)
inf

Theoreminfglbti 6878* An infimum is the greatest lower bound. See also infclti 6876 and inflbti 6877. (Contributed by Jim Kingdon, 18-Dec-2021.)
inf

Theoreminfnlbti 6879* A lower bound is not greater than the infimum. (Contributed by Jim Kingdon, 18-Dec-2021.)
inf

Theoreminfminti 6880* The smallest element of a set is its infimum. Note that the converse is not true; the infimum might not be an element of the set considered. (Contributed by Jim Kingdon, 18-Dec-2021.)
inf

Theoreminfmoti 6881* Any class has at most one infimum in (where is interpreted as 'less than'). (Contributed by Jim Kingdon, 18-Dec-2021.)

Theoreminfeuti 6882* An infimum is unique. (Contributed by Jim Kingdon, 19-Dec-2021.)

Theoreminfsnti 6883* The infimum of a singleton. (Contributed by Jim Kingdon, 19-Dec-2021.)
inf

Theoreminf00 6884 The infimum regarding an empty base set is always the empty set. (Contributed by AV, 4-Sep-2020.)
inf

Theoreminfisoti 6885* Image of an infimum under an isomorphism. (Contributed by Jim Kingdon, 19-Dec-2021.)
inf inf

2.6.34  Ordinal isomorphism

Theoremordiso2 6886 Generalize ordiso 6887 to proper classes. (Contributed by Mario Carneiro, 24-Jun-2015.)

Theoremordiso 6887* Order-isomorphic ordinal numbers are equal. (Contributed by Jeff Hankins, 16-Oct-2009.) (Proof shortened by Mario Carneiro, 24-Jun-2015.)

2.6.35  Disjoint union

2.6.35.1  Disjoint union

Syntaxcdju 6888 Extend class notation to include disjoint union of two classes.

Definitiondf-dju 6889 Disjoint union of two classes. This is a way of creating a class which contains elements corresponding to each element of or , tagging each one with whether it came from or . (Contributed by Jim Kingdon, 20-Jun-2022.)

Theoremdjueq12 6890 Equality theorem for disjoint union. (Contributed by Jim Kingdon, 23-Jun-2022.)

Theoremdjueq1 6891 Equality theorem for disjoint union. (Contributed by Jim Kingdon, 23-Jun-2022.)

Theoremdjueq2 6892 Equality theorem for disjoint union. (Contributed by Jim Kingdon, 23-Jun-2022.)

Theoremnfdju 6893 Bound-variable hypothesis builder for disjoint union. (Contributed by Jim Kingdon, 23-Jun-2022.)

Theoremdjuex 6894 The disjoint union of sets is a set. See also the more precise djuss 6921. (Contributed by AV, 28-Jun-2022.)

Theoremdjuexb 6895 The disjoint union of two classes is a set iff both classes are sets. (Contributed by Jim Kingdon, 6-Sep-2023.)

2.6.35.2  Left and right injections of a disjoint union

In this section, we define the left and right injections of a disjoint union and prove their main properties. These injections are restrictions of the "template" functions inl and inr, which appear in most applications in the form inl and inr .

Syntaxcinl 6896 Extend class notation to include left injection of a disjoint union.
inl

Syntaxcinr 6897 Extend class notation to include right injection of a disjoint union.
inr

Definitiondf-inl 6898 Left injection of a disjoint union. (Contributed by Mario Carneiro, 21-Jun-2022.)
inl

Definitiondf-inr 6899 Right injection of a disjoint union. (Contributed by Mario Carneiro, 21-Jun-2022.)
inr

Theoremdjulclr 6900 Left closure of disjoint union. (Contributed by Jim Kingdon, 21-Jun-2022.) (Revised by BJ, 6-Jul-2022.)
inl

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