P. 74 of Theorem List - Intuitionistic Logic Explorer

Theorem List for Intuitionistic Logic Explorer - 7301-7400   *Has distinct variable group(s)

Type	Label	Description
Statement
Theorem	fsuppcorn 7301	The composition of a 1-1 function with a finitely supported function is finitely supported. The purpose of the ( F supp Z ) C_ ran G condition is to ensure we don't subset the support of the function in such a way as to fun afoul of exmidssfi 7246. (Other alternative conditions might also be sufficient). (Contributed by AV, 28-May-2019.) (Revised by Jim Kingdon, 15-May-2026.)
|- ( ph -> F finSupp Z )   &    |- ( ph -> G : X -1-1-> Y )   &    |- ( ph -> Z e. W )   &    |- ( ph -> F e. V )   &    |- ( ph -> G e. U )   &    |- ( ph -> ( F supp Z ) C_ ran G )   =>    |- ( ph -> ( F o. G ) finSupp Z )
2.6.35  Finite intersections
Syntax	cfi 7302	Extend class notation with the function whose value is the class of finite intersections of the elements of a given set.
class fi
Definition	df-fi 7303*	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 7306). (Contributed by FL, 27-Apr-2008.)
|- fi = ( x e. _V |-> { z | E. y e. ( ~P x i^i Fin ) z = |^| y } )
Theorem	fival 7304*	The set of all the finite intersections of the elements of A. (Contributed by FL, 27-Apr-2008.) (Revised by Mario Carneiro, 24-Nov-2013.)
|- ( A e. V -> ( fi ` A ) = { y | E. x e. ( ~P A i^i Fin ) y = |^| x } )
Theorem	elfi 7305*	Specific properties of an element of ( fi ` B ). (Contributed by FL, 27-Apr-2008.) (Revised by Mario Carneiro, 24-Nov-2013.)
|- ( ( A e. V /\ B e. W ) -> ( A e. ( fi ` B ) <-> E. x e. ( ~P B i^i Fin ) A = |^| x ) )
Theorem	elfi2 7306*	The empty intersection need not be considered in the set of finite intersections. (Contributed by Mario Carneiro, 21-Mar-2015.)
|- ( B e. V -> ( A e. ( fi ` B ) <-> E. x e. ( ( ~P B i^i Fin ) \ { (/) } ) A = |^| x ) )
Theorem	elfir 7307	Sufficient condition for an element of ( fi ` B ). (Contributed by Mario Carneiro, 24-Nov-2013.)
|- ( ( B e. V /\ ( A C_ B /\ A =/= (/) /\ A e. Fin ) ) -> |^| A e. ( fi ` B ) )
Theorem	ssfii 7308	Any element of a set A is the intersection of a finite subset of A. (Contributed by FL, 27-Apr-2008.) (Proof shortened by Mario Carneiro, 21-Mar-2015.)
|- ( A e. V -> A C_ ( fi ` A ) )
Theorem	fi0 7309	The set of finite intersections of the empty set. (Contributed by Mario Carneiro, 30-Aug-2015.)
|- ( fi ` (/) ) = (/)
Theorem	fieq0 7310	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.)
|- ( A e. V -> ( A = (/) <-> ( fi ` A ) = (/) ) )
Theorem	fiss 7311	Subset relationship for function fi. (Contributed by Jeff Hankins, 7-Oct-2009.) (Revised by Mario Carneiro, 24-Nov-2013.)
|- ( ( B e. V /\ A C_ B ) -> ( fi ` A ) C_ ( fi ` B ) )
Theorem	fiuni 7312	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.)
|- ( A e. V -> U. A = U. ( fi ` A ) )
Theorem	fipwssg 7313	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.)
|- ( ( A e. V /\ A C_ ~P X ) -> ( fi ` A ) C_ ~P X )
Theorem	fifo 7314*	Describe a surjection from nonempty finite sets to finite intersections. (Contributed by Mario Carneiro, 18-May-2015.)
|- F = ( y e. ( ( ~P A i^i Fin ) \ { (/) } ) |-> |^| y )   =>    |- ( A e. V -> F : ( ( ~P A i^i Fin ) \ { (/) } ) -onto-> ( fi ` A ) )
Theorem	dcfi 7315*	Decidability of a family of propositions indexed by a finite set. (Contributed by Jim Kingdon, 30-Sep-2024.)
|- ( ( A e. Fin /\ A. x e. A DECID ph ) -> DECID A. x e. A ph )
Theorem	fdcf1 7316	It is decidable whether a function from a finite set into another finite set is one-to-one. (Contributed by Jim Kingdon, 13-Jul-2026.)
|- ( ( A e. Fin /\ B e. Fin /\ F : A --> B ) -> DECID F : A -1-1-> B )
Theorem	f1setfi 7317*	The set of injections between two finite sets is finite. (Contributed by Jim Kingdon, 13-Jul-2026.)
|- ( ( A e. Fin /\ B e. Fin ) -> { f | f : A -1-1-> B } e. Fin )
2.6.36  The sizes of sets
Theorem	2omap 7318*	Mapping between ( 2o ^m A ) and decidable subsets of A. (Contributed by Jim Kingdon, 12-Nov-2025.)
|- F = ( s e. ( 2o ^m A ) |-> { z e. A | ( s ` z ) = 1o } )   =>    |- ( A e. V -> F : ( 2o ^m A ) -1-1-onto-> { x e. ~P A | A. y e. A DECID y e. x } )
Theorem	2omapen 7319*	Equinumerosity of ( 2o ^m A ) and the set of decidable subsets of A. (Contributed by Jim Kingdon, 14-Nov-2025.)
|- ( A e. V -> ( 2o ^m A ) ~~ { x e. ~P A | A. y e. A DECID y e. x } )
Theorem	2omapfi 7320	The number of finite subsets of a finite set. For a similar theorem with set size expressed using ♯ (df-ihash 11215), see hashpwfi 11269. (Contributed by Jim Kingdon, 18-May-2026.)
|- ( A e. Fin -> ( 2o ^m A ) ~~ ( ~P A i^i Fin ) )
Theorem	fipwfi 7321	The set of finite subsets of a finite set is finite. (Contributed by Jim Kingdon, 19-May-2026.)
|- ( A e. Fin -> ( ~P A i^i Fin ) e. Fin )
2.6.37  Supremum and infimum
Syntax	csup 7322	Extend class notation to include supremum of class A. Here R is ordinarily a relation that strictly orders class B. For example, R could be 'less than' and B could be the set of real numbers.
class sup ( A , B , R )
Syntax	cinf 7323	Extend class notation to include infimum of class A. Here R is ordinarily a relation that strictly orders class B. For example, R could be 'less than' and B could be the set of real numbers.
class inf ( A , B , R )
Definition	df-sup 7324*	Define the supremum of class A. It is meaningful when R is a relation that strictly orders B and when the supremum exists. (Contributed by NM, 22-May-1999.)
|- sup ( A , B , R ) = U. { x e. B | ( A. y e. A -. x R y /\ A. y e. B ( y R x -> E. z e. A y R z ) ) }
Definition	df-inf 7325	Define the infimum of class A. It is meaningful when R is a relation that strictly orders B and when the infimum exists. For example, R could be 'less than', B could be the set of real numbers, and A 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 ( A , B , R ) = sup ( A , B , `' R )
Theorem	supeq1 7326	Equality theorem for supremum. (Contributed by NM, 22-May-1999.)
|- ( B = C -> sup ( B , A , R ) = sup ( C , A , R ) )
Theorem	supeq1d 7327	Equality deduction for supremum. (Contributed by Paul Chapman, 22-Jun-2011.)
|- ( ph -> B = C )   =>    |- ( ph -> sup ( B , A , R ) = sup ( C , A , R ) )
Theorem	supeq1i 7328	Equality inference for supremum. (Contributed by Paul Chapman, 22-Jun-2011.)
|- B = C   =>    |- sup ( B , A , R ) = sup ( C , A , R )
Theorem	supeq2 7329	Equality theorem for supremum. (Contributed by Jeff Madsen, 2-Sep-2009.)
|- ( B = C -> sup ( A , B , R ) = sup ( A , C , R ) )
Theorem	supeq3 7330	Equality theorem for supremum. (Contributed by Scott Fenton, 13-Jun-2018.)
|- ( R = S -> sup ( A , B , R ) = sup ( A , B , S ) )
Theorem	supeq123d 7331	Equality deduction for supremum. (Contributed by Stefan O'Rear, 20-Jan-2015.)
|- ( ph -> A = D )   &    |- ( ph -> B = E )   &    |- ( ph -> C = F )   =>    |- ( ph -> sup ( A , B , C ) = sup ( D , E , F ) )
Theorem	nfsup 7332	Hypothesis builder for supremum. (Contributed by Mario Carneiro, 20-Mar-2014.)
|- F/_ x A   &    |- F/_ x B   &    |- F/_ x R   =>    |- F/_ x sup ( A , B , R )
Theorem	supmoti 7333*	Any class B has at most one supremum in A (where R is interpreted as 'less than'). The hypothesis is satisfied by real numbers (see lttri3 8405) or other orders which correspond to tight apartnesses. (Contributed by Jim Kingdon, 23-Nov-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   =>    |- ( ph -> E* x e. A ( A. y e. B -. x R y /\ A. y e. A ( y R x -> E. z e. B y R z ) ) )
Theorem	supeuti 7334*	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.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> E. x e. A ( A. y e. B -. x R y /\ A. y e. A ( y R x -> E. z e. B y R z ) ) )   =>    |- ( ph -> E! x e. A ( A. y e. B -. x R y /\ A. y e. A ( y R x -> E. z e. B y R z ) ) )
Theorem	supval2ti 7335*	Alternate expression for the supremum. (Contributed by Jim Kingdon, 23-Nov-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> E. x e. A ( A. y e. B -. x R y /\ A. y e. A ( y R x -> E. z e. B y R z ) ) )   =>    |- ( ph -> sup ( B , A , R ) = ( iota_ x e. A ( A. y e. B -. x R y /\ A. y e. A ( y R x -> E. z e. B y R z ) ) ) )
Theorem	eqsupti 7336*	Sufficient condition for an element to be equal to the supremum. (Contributed by Jim Kingdon, 23-Nov-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   =>    |- ( ph -> ( ( C e. A /\ A. y e. B -. C R y /\ A. y e. A ( y R C -> E. z e. B y R z ) ) -> sup ( B , A , R ) = C ) )
Theorem	eqsuptid 7337*	Sufficient condition for an element to be equal to the supremum. (Contributed by Jim Kingdon, 24-Nov-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> C e. A )   &    |- ( ( ph /\ y e. B ) -> -. C R y )   &    |- ( ( ph /\ ( y e. A /\ y R C ) ) -> E. z e. B y R z )   =>    |- ( ph -> sup ( B , A , R ) = C )
Theorem	supclti 7338*	A supremum belongs to its base class (closure law). See also supubti 7339 and suplubti 7340. (Contributed by Jim Kingdon, 24-Nov-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> E. x e. A ( A. y e. B -. x R y /\ A. y e. A ( y R x -> E. z e. B y R z ) ) )   =>    |- ( ph -> sup ( B , A , R ) e. A )
Theorem	supubti 7339*	A supremum is an upper bound. See also supclti 7338 and suplubti 7340. This proof demonstrates how to expand an iota-based definition (df-iota 5337) using riotacl2 6053. (Contributed by Jim Kingdon, 24-Nov-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> E. x e. A ( A. y e. B -. x R y /\ A. y e. A ( y R x -> E. z e. B y R z ) ) )   =>    |- ( ph -> ( C e. B -> -. sup ( B , A , R ) R C ) )
Theorem	suplubti 7340*	A supremum is the least upper bound. See also supclti 7338 and supubti 7339. (Contributed by Jim Kingdon, 24-Nov-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> E. x e. A ( A. y e. B -. x R y /\ A. y e. A ( y R x -> E. z e. B y R z ) ) )   =>    |- ( ph -> ( ( C e. A /\ C R sup ( B , A , R ) ) -> E. z e. B C R z ) )
Theorem	suplub2ti 7341*	Bidirectional form of suplubti 7340. (Contributed by Jim Kingdon, 17-Jan-2022.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> E. x e. A ( A. y e. B -. x R y /\ A. y e. A ( y R x -> E. z e. B y R z ) ) )   &    |- ( ph -> R Or A )   &    |- ( ph -> B C_ A )   =>    |- ( ( ph /\ C e. A ) -> ( C R sup ( B , A , R ) <-> E. z e. B C R z ) )
Theorem	supelti 7342*	Supremum membership in a set. (Contributed by Jim Kingdon, 16-Jan-2022.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> E. x e. C ( A. y e. B -. x R y /\ A. y e. A ( y R x -> E. z e. B y R z ) ) )   &    |- ( ph -> C C_ A )   =>    |- ( ph -> sup ( B , A , R ) e. C )
Theorem	sup00 7343	The supremum under an empty base set is always the empty set. (Contributed by AV, 4-Sep-2020.)
|- sup ( B , (/) , R ) = (/)
Theorem	supmaxti 7344*	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.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> C e. A )   &    |- ( ph -> C e. B )   &    |- ( ( ph /\ y e. B ) -> -. C R y )   =>    |- ( ph -> sup ( B , A , R ) = C )
Theorem	supsnti 7345*	The supremum of a singleton. (Contributed by Jim Kingdon, 26-Nov-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> B e. A )   =>    |- ( ph -> sup ( { B } , A , R ) = B )
Theorem	isotilem 7346*	Lemma for isoti 7347. (Contributed by Jim Kingdon, 26-Nov-2021.)
|- ( F Isom R , S ( A , B ) -> ( A. x e. B A. y e. B ( x = y <-> ( -. x S y /\ -. y S x ) ) -> A. u e. A A. v e. A ( u = v <-> ( -. u R v /\ -. v R u ) ) ) )
Theorem	isoti 7347*	An isomorphism preserves tightness. (Contributed by Jim Kingdon, 26-Nov-2021.)
|- ( F Isom R , S ( A , B ) -> ( A. u e. A A. v e. A ( u = v <-> ( -. u R v /\ -. v R u ) ) <-> A. u e. B A. v e. B ( u = v <-> ( -. u S v /\ -. v S u ) ) ) )
Theorem	supisolem 7348*	Lemma for supisoti 7350. (Contributed by Mario Carneiro, 24-Dec-2016.)
|- ( ph -> F Isom R , S ( A , B ) )   &    |- ( ph -> C C_ A )   =>    |- ( ( ph /\ D e. A ) -> ( ( A. y e. C -. D R y /\ A. y e. A ( y R D -> E. z e. C y R z ) ) <-> ( A. w e. ( F " C ) -. ( F ` D ) S w /\ A. w e. B ( w S ( F ` D ) -> E. v e. ( F " C ) w S v ) ) ) )
Theorem	supisoex 7349*	Lemma for supisoti 7350. (Contributed by Mario Carneiro, 24-Dec-2016.)
|- ( ph -> F Isom R , S ( A , B ) )   &    |- ( ph -> C C_ A )   &    |- ( ph -> E. x e. A ( A. y e. C -. x R y /\ A. y e. A ( y R x -> E. z e. C y R z ) ) )   =>    |- ( ph -> E. u e. B ( A. w e. ( F " C ) -. u S w /\ A. w e. B ( w S u -> E. v e. ( F " C ) w S v ) ) )
Theorem	supisoti 7350*	Image of a supremum under an isomorphism. (Contributed by Jim Kingdon, 26-Nov-2021.)
|- ( ph -> F Isom R , S ( A , B ) )   &    |- ( ph -> C C_ A )   &    |- ( ph -> E. x e. A ( A. y e. C -. x R y /\ A. y e. A ( y R x -> E. z e. C y R z ) ) )   &    |- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   =>    |- ( ph -> sup ( ( F " C ) , B , S ) = ( F ` sup ( C , A , R ) ) )
Theorem	infeq1 7351	Equality theorem for infimum. (Contributed by AV, 2-Sep-2020.)
|- ( B = C -> inf ( B , A , R ) = inf ( C , A , R ) )
Theorem	infeq1d 7352	Equality deduction for infimum. (Contributed by AV, 2-Sep-2020.)
|- ( ph -> B = C )   =>    |- ( ph -> inf ( B , A , R ) = inf ( C , A , R ) )
Theorem	infeq1i 7353	Equality inference for infimum. (Contributed by AV, 2-Sep-2020.)
|- B = C   =>    |- inf ( B , A , R ) = inf ( C , A , R )
Theorem	infeq2 7354	Equality theorem for infimum. (Contributed by AV, 2-Sep-2020.)
|- ( B = C -> inf ( A , B , R ) = inf ( A , C , R ) )
Theorem	infeq3 7355	Equality theorem for infimum. (Contributed by AV, 2-Sep-2020.)
|- ( R = S -> inf ( A , B , R ) = inf ( A , B , S ) )
Theorem	infeq123d 7356	Equality deduction for infimum. (Contributed by AV, 2-Sep-2020.)
|- ( ph -> A = D )   &    |- ( ph -> B = E )   &    |- ( ph -> C = F )   =>    |- ( ph -> inf ( A , B , C ) = inf ( D , E , F ) )
Theorem	nfinf 7357	Hypothesis builder for infimum. (Contributed by AV, 2-Sep-2020.)
|- F/_ x A   &    |- F/_ x B   &    |- F/_ x R   =>    |- F/_ xinf ( A , B , R )
Theorem	cnvinfex 7358*	Two ways of expressing existence of an infimum (one in terms of converse). (Contributed by Jim Kingdon, 17-Dec-2021.)
|- ( ph -> E. x e. A ( A. y e. B -. y R x /\ A. y e. A ( x R y -> E. z e. B z R y ) ) )   =>    |- ( ph -> E. x e. A ( A. y e. B -. x `' R y /\ A. y e. A ( y `' R x -> E. z e. B y `' R z ) ) )
Theorem	cnvti 7359*	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.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   =>    |- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u `' R v /\ -. v `' R u ) ) )
Theorem	eqinfti 7360*	Sufficient condition for an element to be equal to the infimum. (Contributed by Jim Kingdon, 16-Dec-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   =>    |- ( ph -> ( ( C e. A /\ A. y e. B -. y R C /\ A. y e. A ( C R y -> E. z e. B z R y ) ) -> inf ( B , A , R ) = C ) )
Theorem	eqinftid 7361*	Sufficient condition for an element to be equal to the infimum. (Contributed by Jim Kingdon, 16-Dec-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> C e. A )   &    |- ( ( ph /\ y e. B ) -> -. y R C )   &    |- ( ( ph /\ ( y e. A /\ C R y ) ) -> E. z e. B z R y )   =>    |- ( ph -> inf ( B , A , R ) = C )
Theorem	infvalti 7362*	Alternate expression for the infimum. (Contributed by Jim Kingdon, 17-Dec-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> E. x e. A ( A. y e. B -. y R x /\ A. y e. A ( x R y -> E. z e. B z R y ) ) )   =>    |- ( ph -> inf ( B , A , R ) = ( iota_ x e. A ( A. y e. B -. y R x /\ A. y e. A ( x R y -> E. z e. B z R y ) ) ) )
Theorem	infclti 7363*	An infimum belongs to its base class (closure law). See also inflbti 7364 and infglbti 7365. (Contributed by Jim Kingdon, 17-Dec-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> E. x e. A ( A. y e. B -. y R x /\ A. y e. A ( x R y -> E. z e. B z R y ) ) )   =>    |- ( ph -> inf ( B , A , R ) e. A )
Theorem	inflbti 7364*	An infimum is a lower bound. See also infclti 7363 and infglbti 7365. (Contributed by Jim Kingdon, 18-Dec-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> E. x e. A ( A. y e. B -. y R x /\ A. y e. A ( x R y -> E. z e. B z R y ) ) )   =>    |- ( ph -> ( C e. B -> -. C Rinf ( B , A , R ) ) )
Theorem	infglbti 7365*	An infimum is the greatest lower bound. See also infclti 7363 and inflbti 7364. (Contributed by Jim Kingdon, 18-Dec-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> E. x e. A ( A. y e. B -. y R x /\ A. y e. A ( x R y -> E. z e. B z R y ) ) )   =>    |- ( ph -> ( ( C e. A /\ inf ( B , A , R ) R C ) -> E. z e. B z R C ) )
Theorem	infnlbti 7366*	A lower bound is not greater than the infimum. (Contributed by Jim Kingdon, 18-Dec-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> E. x e. A ( A. y e. B -. y R x /\ A. y e. A ( x R y -> E. z e. B z R y ) ) )   =>    |- ( ph -> ( ( C e. A /\ A. z e. B -. z R C ) -> -. inf ( B , A , R ) R C ) )
Theorem	infminti 7367*	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.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> C e. A )   &    |- ( ph -> C e. B )   &    |- ( ( ph /\ y e. B ) -> -. y R C )   =>    |- ( ph -> inf ( B , A , R ) = C )
Theorem	infmoti 7368*	Any class B has at most one infimum in A (where R is interpreted as 'less than'). (Contributed by Jim Kingdon, 18-Dec-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   =>    |- ( ph -> E* x e. A ( A. y e. B -. y R x /\ A. y e. A ( x R y -> E. z e. B z R y ) ) )
Theorem	infeuti 7369*	An infimum is unique. (Contributed by Jim Kingdon, 19-Dec-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> E. x e. A ( A. y e. B -. y R x /\ A. y e. A ( x R y -> E. z e. B z R y ) ) )   =>    |- ( ph -> E! x e. A ( A. y e. B -. y R x /\ A. y e. A ( x R y -> E. z e. B z R y ) ) )
Theorem	infsnti 7370*	The infimum of a singleton. (Contributed by Jim Kingdon, 19-Dec-2021.)
|- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   &    |- ( ph -> B e. A )   =>    |- ( ph -> inf ( { B } , A , R ) = B )
Theorem	inf00 7371	The infimum regarding an empty base set is always the empty set. (Contributed by AV, 4-Sep-2020.)
|- inf ( B , (/) , R ) = (/)
Theorem	infisoti 7372*	Image of an infimum under an isomorphism. (Contributed by Jim Kingdon, 19-Dec-2021.)
|- ( ph -> F Isom R , S ( A , B ) )   &    |- ( ph -> C C_ A )   &    |- ( ph -> E. x e. A ( A. y e. C -. y R x /\ A. y e. A ( x R y -> E. z e. C z R y ) ) )   &    |- ( ( ph /\ ( u e. A /\ v e. A ) ) -> ( u = v <-> ( -. u R v /\ -. v R u ) ) )   =>    |- ( ph -> inf ( ( F " C ) , B , S ) = ( F ` inf ( C , A , R ) ) )
Theorem	supex2g 7373	Existence of supremum. (Contributed by Jeff Madsen, 2-Sep-2009.)
|- ( A e. C -> sup ( B , A , R ) e. _V )
Theorem	infex2g 7374	Existence of infimum. (Contributed by Jim Kingdon, 1-Oct-2024.)
|- ( A e. C -> inf ( B , A , R ) e. _V )
2.6.38  Ordinal isomorphism
Theorem	ordiso2 7375	Generalize ordiso 7376 to proper classes. (Contributed by Mario Carneiro, 24-Jun-2015.)
|- ( ( F Isom _E , _E ( A , B ) /\ Ord A /\ Ord B ) -> A = B )
Theorem	ordiso 7376*	Order-isomorphic ordinal numbers are equal. (Contributed by Jeff Hankins, 16-Oct-2009.) (Proof shortened by Mario Carneiro, 24-Jun-2015.)
|- ( ( A e. On /\ B e. On ) -> ( A = B <-> E. f f Isom _E , _E ( A , B ) ) )
2.6.39  Disjoint union
2.6.39.1  Disjoint union
Syntax	cdju 7377	Extend class notation to include disjoint union of two classes.
class ( A ⊔ B )
Definition	df-dju 7378	Disjoint union of two classes. This is a way of creating a class which contains elements corresponding to each element of A or B, tagging each one with whether it came from A or B. (Contributed by Jim Kingdon, 20-Jun-2022.)
|- ( A ⊔ B ) = ( ( { (/) } X. A ) u. ( { 1o } X. B ) )
Theorem	djueq12 7379	Equality theorem for disjoint union. (Contributed by Jim Kingdon, 23-Jun-2022.)
|- ( ( A = B /\ C = D ) -> ( A ⊔ C ) = ( B ⊔ D ) )
Theorem	djueq1 7380	Equality theorem for disjoint union. (Contributed by Jim Kingdon, 23-Jun-2022.)
|- ( A = B -> ( A ⊔ C ) = ( B ⊔ C ) )
Theorem	djueq2 7381	Equality theorem for disjoint union. (Contributed by Jim Kingdon, 23-Jun-2022.)
|- ( A = B -> ( C ⊔ A ) = ( C ⊔ B ) )
Theorem	nfdju 7382	Bound-variable hypothesis builder for disjoint union. (Contributed by Jim Kingdon, 23-Jun-2022.)
|- F/_ x A   &    |- F/_ x B   =>    |- F/_ x ( A ⊔ B )
Theorem	djuex 7383	The disjoint union of sets is a set. See also the more precise djuss 7410. (Contributed by AV, 28-Jun-2022.)
|- ( ( A e. V /\ B e. W ) -> ( A ⊔ B ) e. _V )
Theorem	djuexb 7384	The disjoint union of two classes is a set iff both classes are sets. (Contributed by Jim Kingdon, 6-Sep-2023.)
|- ( ( A e. _V /\ B e. _V ) <-> ( A ⊔ B ) e. _V )
2.6.39.2  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 |` A ) and (inr |` B ).
Syntax	cinl 7385	Extend class notation to include left injection of a disjoint union.
class inl
Syntax	cinr 7386	Extend class notation to include right injection of a disjoint union.
class inr
Definition	df-inl 7387	Left injection of a disjoint union. (Contributed by Mario Carneiro, 21-Jun-2022.)
|- inl = ( x e. _V |-> <. (/) , x >. )
Definition	df-inr 7388	Right injection of a disjoint union. (Contributed by Mario Carneiro, 21-Jun-2022.)
|- inr = ( x e. _V |-> <. 1o , x >. )
Theorem	djulclr 7389	Left closure of disjoint union. (Contributed by Jim Kingdon, 21-Jun-2022.) (Revised by BJ, 6-Jul-2022.)
|- ( C e. A -> ( (inl |` A ) ` C ) e. ( A ⊔ B ) )
Theorem	djurclr 7390	Right closure of disjoint union. (Contributed by Jim Kingdon, 21-Jun-2022.) (Revised by BJ, 6-Jul-2022.)
|- ( C e. B -> ( (inr |` B ) ` C ) e. ( A ⊔ B ) )
Theorem	djulcl 7391	Left closure of disjoint union. (Contributed by Jim Kingdon, 21-Jun-2022.)
|- ( C e. A -> (inl ` C ) e. ( A ⊔ B ) )
Theorem	djurcl 7392	Right closure of disjoint union. (Contributed by Jim Kingdon, 21-Jun-2022.)
|- ( C e. B -> (inr ` C ) e. ( A ⊔ B ) )
Theorem	djuf1olem 7393*	Lemma for djulf1o 7398 and djurf1o 7399. (Contributed by BJ and Jim Kingdon, 4-Jul-2022.)
|- X e. _V   &    |- F = ( x e. A |-> <. X , x >. )   =>    |- F : A -1-1-onto-> ( { X } X. A )
Theorem	djuf1olemr 7394*	Lemma for djulf1or 7396 and djurf1or 7397. For a version of this lemma with F defined on A and no restriction in the conclusion, see djuf1olem 7393. (Contributed by BJ and Jim Kingdon, 4-Jul-2022.)
|- X e. _V   &    |- F = ( x e. _V |-> <. X , x >. )   =>    |- ( F |` A ) : A -1-1-onto-> ( { X } X. A )
Theorem	djulclb 7395	Left biconditional closure of disjoint union. (Contributed by Jim Kingdon, 2-Jul-2022.)
|- ( C e. V -> ( C e. A <-> (inl ` C ) e. ( A ⊔ B ) ) )
Theorem	djulf1or 7396	The left injection function on all sets is one to one and onto. (Contributed by BJ and Jim Kingdon, 22-Jun-2022.)
|- (inl |` A ) : A -1-1-onto-> ( { (/) } X. A )
Theorem	djurf1or 7397	The right injection function on all sets is one to one and onto. (Contributed by BJ and Jim Kingdon, 22-Jun-2022.)
|- (inr |` A ) : A -1-1-onto-> ( { 1o } X. A )
Theorem	djulf1o 7398	The left injection function on all sets is one to one and onto. (Contributed by Jim Kingdon, 22-Jun-2022.)
|- inl : _V -1-1-onto-> ( { (/) } X. _V )
Theorem	djurf1o 7399	The right injection function on all sets is one to one and onto. (Contributed by Jim Kingdon, 22-Jun-2022.)
|- inr : _V -1-1-onto-> ( { 1o } X. _V )
Theorem	inresflem 7400*	Lemma for inlresf1 7401 and inrresf1 7402. (Contributed by BJ, 4-Jul-2022.)
|- F : A -1-1-onto-> ( { X } X. A )   &    |- ( x e. A -> ( F ` x ) e. B )   =>    |- F : A -1-1-> B