P. 40 of Theorem List - Intuitionistic Logic Explorer

Theorem List for Intuitionistic Logic Explorer - 3901-4000   *Has distinct variable group(s)

Type	Label	Description
Statement
Theorem	intmin3 3901*	Under subset ordering, the intersection of a class abstraction is less than or equal to any of its members. (Contributed by NM, 3-Jul-2005.)
|- ( x = A -> ( ph <-> ps ) )   &    |- ps   =>    |- ( A e. V -> |^| { x | ph } C_ A )
Theorem	intmin4 3902*	Elimination of a conjunct in a class intersection. (Contributed by NM, 31-Jul-2006.)
|- ( A C_ |^| { x | ph } -> |^| { x | ( A C_ x /\ ph ) } = |^| { x | ph } )
Theorem	intab 3903*	The intersection of a special case of a class abstraction. y may be free in ph and A, which can be thought of a ph ( y ) and A ( y ). (Contributed by NM, 28-Jul-2006.) (Proof shortened by Mario Carneiro, 14-Nov-2016.)
|- A e. _V   &    |- { x | E. y ( ph /\ x = A ) } e. _V   =>    |- |^| { x | A. y ( ph -> A e. x ) } = { x | E. y ( ph /\ x = A ) }
Theorem	int0el 3904	The intersection of a class containing the empty set is empty. (Contributed by NM, 24-Apr-2004.)
|- ( (/) e. A -> |^| A = (/) )
Theorem	intun 3905	The class intersection of the union of two classes. Theorem 78 of [Suppes] p. 42. (Contributed by NM, 22-Sep-2002.)
|- |^| ( A u. B ) = ( |^| A i^i |^| B )
Theorem	intpr 3906	The intersection of a pair is the intersection of its members. Theorem 71 of [Suppes] p. 42. (Contributed by NM, 14-Oct-1999.)
|- A e. _V   &    |- B e. _V   =>    |- |^| { A , B } = ( A i^i B )
Theorem	intprg 3907	The intersection of a pair is the intersection of its members. Closed form of intpr 3906. Theorem 71 of [Suppes] p. 42. (Contributed by FL, 27-Apr-2008.)
|- ( ( A e. V /\ B e. W ) -> |^| { A , B } = ( A i^i B ) )
Theorem	intsng 3908	Intersection of a singleton. (Contributed by Stefan O'Rear, 22-Feb-2015.)
|- ( A e. V -> |^| { A } = A )
Theorem	intsn 3909	The intersection of a singleton is its member. Theorem 70 of [Suppes] p. 41. (Contributed by NM, 29-Sep-2002.)
|- A e. _V   =>    |- |^| { A } = A
Theorem	uniintsnr 3910*	The union and intersection of a singleton are equal. See also eusn 3696. (Contributed by Jim Kingdon, 14-Aug-2018.)
|- ( E. x A = { x } -> U. A = |^| A )
Theorem	uniintabim 3911	The union and the intersection of a class abstraction are equal if there is a unique satisfying value of ph ( x ). (Contributed by Jim Kingdon, 14-Aug-2018.)
|- ( E! x ph -> U. { x | ph } = |^| { x | ph } )
Theorem	intunsn 3912	Theorem joining a singleton to an intersection. (Contributed by NM, 29-Sep-2002.)
|- B e. _V   =>    |- |^| ( A u. { B } ) = ( |^| A i^i B )
Theorem	rint0 3913	Relative intersection of an empty set. (Contributed by Stefan O'Rear, 3-Apr-2015.)
|- ( X = (/) -> ( A i^i |^| X ) = A )
Theorem	elrint 3914*	Membership in a restricted intersection. (Contributed by Stefan O'Rear, 3-Apr-2015.)
|- ( X e. ( A i^i |^| B ) <-> ( X e. A /\ A. y e. B X e. y ) )
Theorem	elrint2 3915*	Membership in a restricted intersection. (Contributed by Stefan O'Rear, 3-Apr-2015.)
|- ( X e. A -> ( X e. ( A i^i |^| B ) <-> A. y e. B X e. y ) )
2.1.20  Indexed union and intersection
Syntax	ciun 3916	Extend class notation to include indexed union. Note: Historically (prior to 21-Oct-2005), set.mm used the notation U. x e. A B, with the same union symbol as cuni 3839. While that syntax was unambiguous, it did not allow for LALR parsing of the syntax constructions in set.mm. The new syntax uses as distinguished symbol U_ instead of U. and does allow LALR parsing. Thanks to Peter Backes for suggesting this change.
class U_ x e. A B
Syntax	ciin 3917	Extend class notation to include indexed intersection. Note: Historically (prior to 21-Oct-2005), set.mm used the notation |^| x e. A B, with the same intersection symbol as cint 3874. Although that syntax was unambiguous, it did not allow for LALR parsing of the syntax constructions in set.mm. The new syntax uses a distinguished symbol |^|_ instead of |^| and does allow LALR parsing. Thanks to Peter Backes for suggesting this change.
class |^|_ x e. A B
Definition	df-iun 3918*	Define indexed union. Definition indexed union in [Stoll] p. 45. In most applications, A is independent of x (although this is not required by the definition), and B depends on x i.e. can be read informally as B ( x ). We call x the index, A the index set, and B the indexed set. In most books, x e. A is written as a subscript or underneath a union symbol U.. We use a special union symbol U_ to make it easier to distinguish from plain class union. In many theorems, you will see that x and A are in the same disjoint variable group (meaning A cannot depend on x) and that B and x do not share a disjoint variable group (meaning that can be thought of as B ( x ) i.e. can be substituted with a class expression containing x). An alternate definition tying indexed union to ordinary union is dfiun2 3950. Theorem uniiun 3970 provides a definition of ordinary union in terms of indexed union. (Contributed by NM, 27-Jun-1998.)
|- U_ x e. A B = { y | E. x e. A y e. B }
Definition	df-iin 3919*	Define indexed intersection. Definition of [Stoll] p. 45. See the remarks for its sibling operation of indexed union df-iun 3918. An alternate definition tying indexed intersection to ordinary intersection is dfiin2 3951. Theorem intiin 3971 provides a definition of ordinary intersection in terms of indexed intersection. (Contributed by NM, 27-Jun-1998.)
|- |^|_ x e. A B = { y | A. x e. A y e. B }
Theorem	eliun 3920*	Membership in indexed union. (Contributed by NM, 3-Sep-2003.)
|- ( A e. U_ x e. B C <-> E. x e. B A e. C )
Theorem	eliin 3921*	Membership in indexed intersection. (Contributed by NM, 3-Sep-2003.)
|- ( A e. V -> ( A e. |^|_ x e. B C <-> A. x e. B A e. C ) )
Theorem	iuncom 3922*	Commutation of indexed unions. (Contributed by NM, 18-Dec-2008.)
|- U_ x e. A U_ y e. B C = U_ y e. B U_ x e. A C
Theorem	iuncom4 3923	Commutation of union with indexed union. (Contributed by Mario Carneiro, 18-Jan-2014.)
|- U_ x e. A U. B = U. U_ x e. A B
Theorem	iunconstm 3924*	Indexed union of a constant class, i.e. where B does not depend on x. (Contributed by Jim Kingdon, 15-Aug-2018.)
|- ( E. x x e. A -> U_ x e. A B = B )
Theorem	iinconstm 3925*	Indexed intersection of a constant class, i.e. where B does not depend on x. (Contributed by Jim Kingdon, 19-Dec-2018.)
|- ( E. y y e. A -> |^|_ x e. A B = B )
Theorem	iuniin 3926*	Law combining indexed union with indexed intersection. Eq. 14 in [KuratowskiMostowski] p. 109. This theorem also appears as the last example at http://en.wikipedia.org/wiki/Union%5F%28set%5Ftheory%29. (Contributed by NM, 17-Aug-2004.) (Proof shortened by Andrew Salmon, 25-Jul-2011.)
|- U_ x e. A |^|_ y e. B C C_ |^|_ y e. B U_ x e. A C
Theorem	iunss1 3927*	Subclass theorem for indexed union. (Contributed by NM, 10-Dec-2004.) (Proof shortened by Andrew Salmon, 25-Jul-2011.)
|- ( A C_ B -> U_ x e. A C C_ U_ x e. B C )
Theorem	iinss1 3928*	Subclass theorem for indexed union. (Contributed by NM, 24-Jan-2012.)
|- ( A C_ B -> |^|_ x e. B C C_ |^|_ x e. A C )
Theorem	iuneq1 3929*	Equality theorem for indexed union. (Contributed by NM, 27-Jun-1998.)
|- ( A = B -> U_ x e. A C = U_ x e. B C )
Theorem	iineq1 3930*	Equality theorem for restricted existential quantifier. (Contributed by NM, 27-Jun-1998.)
|- ( A = B -> |^|_ x e. A C = |^|_ x e. B C )
Theorem	ss2iun 3931	Subclass theorem for indexed union. (Contributed by NM, 26-Nov-2003.) (Proof shortened by Andrew Salmon, 25-Jul-2011.)
|- ( A. x e. A B C_ C -> U_ x e. A B C_ U_ x e. A C )
Theorem	iuneq2 3932	Equality theorem for indexed union. (Contributed by NM, 22-Oct-2003.)
|- ( A. x e. A B = C -> U_ x e. A B = U_ x e. A C )
Theorem	iineq2 3933	Equality theorem for indexed intersection. (Contributed by NM, 22-Oct-2003.) (Proof shortened by Andrew Salmon, 25-Jul-2011.)
|- ( A. x e. A B = C -> |^|_ x e. A B = |^|_ x e. A C )
Theorem	iuneq2i 3934	Equality inference for indexed union. (Contributed by NM, 22-Oct-2003.)
|- ( x e. A -> B = C )   =>    |- U_ x e. A B = U_ x e. A C
Theorem	iineq2i 3935	Equality inference for indexed intersection. (Contributed by NM, 22-Oct-2003.)
|- ( x e. A -> B = C )   =>    |- |^|_ x e. A B = |^|_ x e. A C
Theorem	iineq2d 3936	Equality deduction for indexed intersection. (Contributed by NM, 7-Dec-2011.)
|- F/ x ph   &    |- ( ( ph /\ x e. A ) -> B = C )   =>    |- ( ph -> |^|_ x e. A B = |^|_ x e. A C )
Theorem	iuneq2dv 3937*	Equality deduction for indexed union. (Contributed by NM, 3-Aug-2004.)
|- ( ( ph /\ x e. A ) -> B = C )   =>    |- ( ph -> U_ x e. A B = U_ x e. A C )
Theorem	iineq2dv 3938*	Equality deduction for indexed intersection. (Contributed by NM, 3-Aug-2004.)
|- ( ( ph /\ x e. A ) -> B = C )   =>    |- ( ph -> |^|_ x e. A B = |^|_ x e. A C )
Theorem	iuneq1d 3939*	Equality theorem for indexed union, deduction version. (Contributed by Drahflow, 22-Oct-2015.)
|- ( ph -> A = B )   =>    |- ( ph -> U_ x e. A C = U_ x e. B C )
Theorem	iuneq12d 3940*	Equality deduction for indexed union, deduction version. (Contributed by Drahflow, 22-Oct-2015.)
|- ( ph -> A = B )   &    |- ( ph -> C = D )   =>    |- ( ph -> U_ x e. A C = U_ x e. B D )
Theorem	iuneq2d 3941*	Equality deduction for indexed union. (Contributed by Drahflow, 22-Oct-2015.)
|- ( ph -> B = C )   =>    |- ( ph -> U_ x e. A B = U_ x e. A C )
Theorem	nfiunxy 3942*	Bound-variable hypothesis builder for indexed union. (Contributed by Mario Carneiro, 25-Jan-2014.)
|- F/_ y A   &    |- F/_ y B   =>    |- F/_ y U_ x e. A B
Theorem	nfiinxy 3943*	Bound-variable hypothesis builder for indexed intersection. (Contributed by Mario Carneiro, 25-Jan-2014.)
|- F/_ y A   &    |- F/_ y B   =>    |- F/_ y |^|_ x e. A B
Theorem	nfiunya 3944*	Bound-variable hypothesis builder for indexed union. (Contributed by Mario Carneiro, 25-Jan-2014.)
|- F/_ y A   &    |- F/_ y B   =>    |- F/_ y U_ x e. A B
Theorem	nfiinya 3945*	Bound-variable hypothesis builder for indexed intersection. (Contributed by Mario Carneiro, 25-Jan-2014.)
|- F/_ y A   &    |- F/_ y B   =>    |- F/_ y |^|_ x e. A B
Theorem	nfiu1 3946	Bound-variable hypothesis builder for indexed union. (Contributed by NM, 12-Oct-2003.)
|- F/_ x U_ x e. A B
Theorem	nfii1 3947	Bound-variable hypothesis builder for indexed intersection. (Contributed by NM, 15-Oct-2003.)
|- F/_ x |^|_ x e. A B
Theorem	dfiun2g 3948*	Alternate definition of indexed union when B is a set. Definition 15(a) of [Suppes] p. 44. (Contributed by NM, 23-Mar-2006.) (Proof shortened by Andrew Salmon, 25-Jul-2011.)
|- ( A. x e. A B e. C -> U_ x e. A B = U. { y | E. x e. A y = B } )
Theorem	dfiin2g 3949*	Alternate definition of indexed intersection when B is a set. (Contributed by Jeff Hankins, 27-Aug-2009.)
|- ( A. x e. A B e. C -> |^|_ x e. A B = |^| { y | E. x e. A y = B } )
Theorem	dfiun2 3950*	Alternate definition of indexed union when B is a set. Definition 15(a) of [Suppes] p. 44. (Contributed by NM, 27-Jun-1998.) (Revised by David Abernethy, 19-Jun-2012.)
|- B e. _V   =>    |- U_ x e. A B = U. { y | E. x e. A y = B }
Theorem	dfiin2 3951*	Alternate definition of indexed intersection when B is a set. Definition 15(b) of [Suppes] p. 44. (Contributed by NM, 28-Jun-1998.) (Proof shortened by Andrew Salmon, 25-Jul-2011.)
|- B e. _V   =>    |- |^|_ x e. A B = |^| { y | E. x e. A y = B }
Theorem	dfiunv2 3952*	Define double indexed union. (Contributed by FL, 6-Nov-2013.)
|- U_ x e. A U_ y e. B C = { z | E. x e. A E. y e. B z e. C }
Theorem	cbviun 3953*	Rule used to change the bound variables in an indexed union, with the substitution specified implicitly by the hypothesis. (Contributed by NM, 26-Mar-2006.) (Revised by Andrew Salmon, 25-Jul-2011.)
|- F/_ y B   &    |- F/_ x C   &    |- ( x = y -> B = C )   =>    |- U_ x e. A B = U_ y e. A C
Theorem	cbviin 3954*	Change bound variables in an indexed intersection. (Contributed by Jeff Hankins, 26-Aug-2009.) (Revised by Mario Carneiro, 14-Oct-2016.)
|- F/_ y B   &    |- F/_ x C   &    |- ( x = y -> B = C )   =>    |- |^|_ x e. A B = |^|_ y e. A C
Theorem	cbviunv 3955*	Rule used to change the bound variables in an indexed union, with the substitution specified implicitly by the hypothesis. (Contributed by NM, 15-Sep-2003.)
|- ( x = y -> B = C )   =>    |- U_ x e. A B = U_ y e. A C
Theorem	cbviinv 3956*	Change bound variables in an indexed intersection. (Contributed by Jeff Hankins, 26-Aug-2009.)
|- ( x = y -> B = C )   =>    |- |^|_ x e. A B = |^|_ y e. A C
Theorem	iunss 3957*	Subset theorem for an indexed union. (Contributed by NM, 13-Sep-2003.) (Proof shortened by Andrew Salmon, 25-Jul-2011.)
|- ( U_ x e. A B C_ C <-> A. x e. A B C_ C )
Theorem	ssiun 3958*	Subset implication for an indexed union. (Contributed by NM, 3-Sep-2003.) (Proof shortened by Andrew Salmon, 25-Jul-2011.)
|- ( E. x e. A C C_ B -> C C_ U_ x e. A B )
Theorem	ssiun2 3959	Identity law for subset of an indexed union. (Contributed by NM, 12-Oct-2003.) (Proof shortened by Andrew Salmon, 25-Jul-2011.)
|- ( x e. A -> B C_ U_ x e. A B )
Theorem	ssiun2s 3960*	Subset relationship for an indexed union. (Contributed by NM, 26-Oct-2003.)
|- ( x = C -> B = D )   =>    |- ( C e. A -> D C_ U_ x e. A B )
Theorem	iunss2 3961*	A subclass condition on the members of two indexed classes C ( x ) and D ( y ) that implies a subclass relation on their indexed unions. Generalization of Proposition 8.6 of [TakeutiZaring] p. 59. Compare uniss2 3870. (Contributed by NM, 9-Dec-2004.)
|- ( A. x e. A E. y e. B C C_ D -> U_ x e. A C C_ U_ y e. B D )
Theorem	iunssd 3962*	Subset theorem for an indexed union. (Contributed by Glauco Siliprandi, 8-Apr-2021.)
|- ( ( ph /\ x e. A ) -> B C_ C )   =>    |- ( ph -> U_ x e. A B C_ C )
Theorem	iunab 3963*	The indexed union of a class abstraction. (Contributed by NM, 27-Dec-2004.)
|- U_ x e. A { y | ph } = { y | E. x e. A ph }
Theorem	iunrab 3964*	The indexed union of a restricted class abstraction. (Contributed by NM, 3-Jan-2004.) (Proof shortened by Mario Carneiro, 14-Nov-2016.)
|- U_ x e. A { y e. B | ph } = { y e. B | E. x e. A ph }
Theorem	iunxdif2 3965*	Indexed union with a class difference as its index. (Contributed by NM, 10-Dec-2004.)
|- ( x = y -> C = D )   =>    |- ( A. x e. A E. y e. ( A \ B ) C C_ D -> U_ y e. ( A \ B ) D = U_ x e. A C )
Theorem	ssiinf 3966	Subset theorem for an indexed intersection. (Contributed by FL, 15-Oct-2012.) (Proof shortened by Mario Carneiro, 14-Oct-2016.)
|- F/_ x C   =>    |- ( C C_ |^|_ x e. A B <-> A. x e. A C C_ B )
Theorem	ssiin 3967*	Subset theorem for an indexed intersection. (Contributed by NM, 15-Oct-2003.)
|- ( C C_ |^|_ x e. A B <-> A. x e. A C C_ B )
Theorem	iinss 3968*	Subset implication for an indexed intersection. (Contributed by NM, 15-Oct-2003.) (Proof shortened by Andrew Salmon, 25-Jul-2011.)
|- ( E. x e. A B C_ C -> |^|_ x e. A B C_ C )
Theorem	iinss2 3969	An indexed intersection is included in any of its members. (Contributed by FL, 15-Oct-2012.)
|- ( x e. A -> |^|_ x e. A B C_ B )
Theorem	uniiun 3970*	Class union in terms of indexed union. Definition in [Stoll] p. 43. (Contributed by NM, 28-Jun-1998.)
|- U. A = U_ x e. A x
Theorem	intiin 3971*	Class intersection in terms of indexed intersection. Definition in [Stoll] p. 44. (Contributed by NM, 28-Jun-1998.)
|- |^| A = |^|_ x e. A x
Theorem	iunid 3972*	An indexed union of singletons recovers the index set. (Contributed by NM, 6-Sep-2005.)
|- U_ x e. A { x } = A
Theorem	iun0 3973	An indexed union of the empty set is empty. (Contributed by NM, 26-Mar-2003.) (Proof shortened by Andrew Salmon, 25-Jul-2011.)
|- U_ x e. A (/) = (/)
Theorem	0iun 3974	An empty indexed union is empty. (Contributed by NM, 4-Dec-2004.) (Proof shortened by Andrew Salmon, 25-Jul-2011.)
|- U_ x e. (/) A = (/)
Theorem	0iin 3975	An empty indexed intersection is the universal class. (Contributed by NM, 20-Oct-2005.)
|- |^|_ x e. (/) A = _V
Theorem	viin 3976*	Indexed intersection with a universal index class. (Contributed by NM, 11-Sep-2008.)
|- |^|_ x e. _V A = { y | A. x y e. A }
Theorem	iunn0m 3977*	There is an inhabited class in an indexed collection B ( x ) iff the indexed union of them is inhabited. (Contributed by Jim Kingdon, 16-Aug-2018.)
|- ( E. x e. A E. y y e. B <-> E. y y e. U_ x e. A B )
Theorem	iinab 3978*	Indexed intersection of a class builder. (Contributed by NM, 6-Dec-2011.)
|- |^|_ x e. A { y | ph } = { y | A. x e. A ph }
Theorem	iinrabm 3979*	Indexed intersection of a restricted class builder. (Contributed by Jim Kingdon, 16-Aug-2018.)
|- ( E. x x e. A -> |^|_ x e. A { y e. B | ph } = { y e. B | A. x e. A ph } )
Theorem	iunin2 3980*	Indexed union of intersection. Generalization of half of theorem "Distributive laws" in [Enderton] p. 30. Use uniiun 3970 to recover Enderton's theorem. (Contributed by NM, 26-Mar-2004.)
|- U_ x e. A ( B i^i C ) = ( B i^i U_ x e. A C )
Theorem	iunin1 3981*	Indexed union of intersection. Generalization of half of theorem "Distributive laws" in [Enderton] p. 30. Use uniiun 3970 to recover Enderton's theorem. (Contributed by Mario Carneiro, 30-Aug-2015.)
|- U_ x e. A ( C i^i B ) = ( U_ x e. A C i^i B )
Theorem	iundif2ss 3982*	Indexed union of class difference. Compare to theorem "De Morgan's laws" in [Enderton] p. 31. (Contributed by Jim Kingdon, 17-Aug-2018.)
|- U_ x e. A ( B \ C ) C_ ( B \ |^|_ x e. A C )
Theorem	2iunin 3983*	Rearrange indexed unions over intersection. (Contributed by NM, 18-Dec-2008.)
|- U_ x e. A U_ y e. B ( C i^i D ) = ( U_ x e. A C i^i U_ y e. B D )
Theorem	iindif2m 3984*	Indexed intersection of class difference. Compare to Theorem "De Morgan's laws" in [Enderton] p. 31. (Contributed by Jim Kingdon, 17-Aug-2018.)
|- ( E. x x e. A -> |^|_ x e. A ( B \ C ) = ( B \ U_ x e. A C ) )
Theorem	iinin2m 3985*	Indexed intersection of intersection. Compare to Theorem "Distributive laws" in [Enderton] p. 30. (Contributed by Jim Kingdon, 17-Aug-2018.)
|- ( E. x x e. A -> |^|_ x e. A ( B i^i C ) = ( B i^i |^|_ x e. A C ) )
Theorem	iinin1m 3986*	Indexed intersection of intersection. Compare to Theorem "Distributive laws" in [Enderton] p. 30. (Contributed by Jim Kingdon, 17-Aug-2018.)
|- ( E. x x e. A -> |^|_ x e. A ( C i^i B ) = ( |^|_ x e. A C i^i B ) )
Theorem	elriin 3987*	Elementhood in a relative intersection. (Contributed by Mario Carneiro, 30-Dec-2016.)
|- ( B e. ( A i^i |^|_ x e. X S ) <-> ( B e. A /\ A. x e. X B e. S ) )
Theorem	riin0 3988*	Relative intersection of an empty family. (Contributed by Stefan O'Rear, 3-Apr-2015.)
|- ( X = (/) -> ( A i^i |^|_ x e. X S ) = A )
Theorem	riinm 3989*	Relative intersection of an inhabited family. (Contributed by Jim Kingdon, 19-Aug-2018.)
|- ( ( A. x e. X S C_ A /\ E. x x e. X ) -> ( A i^i |^|_ x e. X S ) = |^|_ x e. X S )
Theorem	iinxsng 3990*	A singleton index picks out an instance of an indexed intersection's argument. (Contributed by NM, 15-Jan-2012.) (Proof shortened by Mario Carneiro, 17-Nov-2016.)
|- ( x = A -> B = C )   =>    |- ( A e. V -> |^|_ x e. { A } B = C )
Theorem	iinxprg 3991*	Indexed intersection with an unordered pair index. (Contributed by NM, 25-Jan-2012.)
|- ( x = A -> C = D )   &    |- ( x = B -> C = E )   =>    |- ( ( A e. V /\ B e. W ) -> |^|_ x e. { A , B } C = ( D i^i E ) )
Theorem	iunxsng 3992*	A singleton index picks out an instance of an indexed union's argument. (Contributed by Mario Carneiro, 25-Jun-2016.)
|- ( x = A -> B = C )   =>    |- ( A e. V -> U_ x e. { A } B = C )
Theorem	iunxsn 3993*	A singleton index picks out an instance of an indexed union's argument. (Contributed by NM, 26-Mar-2004.) (Proof shortened by Mario Carneiro, 25-Jun-2016.)
|- A e. _V   &    |- ( x = A -> B = C )   =>    |- U_ x e. { A } B = C
Theorem	iunxsngf 3994*	A singleton index picks out an instance of an indexed union's argument. (Contributed by Mario Carneiro, 25-Jun-2016.) (Revised by Thierry Arnoux, 2-May-2020.)
|- F/_ x C   &    |- ( x = A -> B = C )   =>    |- ( A e. V -> U_ x e. { A } B = C )
Theorem	iunun 3995	Separate a union in an indexed union. (Contributed by NM, 27-Dec-2004.) (Proof shortened by Mario Carneiro, 17-Nov-2016.)
|- U_ x e. A ( B u. C ) = ( U_ x e. A B u. U_ x e. A C )
Theorem	iunxun 3996	Separate a union in the index of an indexed union. (Contributed by NM, 26-Mar-2004.) (Proof shortened by Mario Carneiro, 17-Nov-2016.)
|- U_ x e. ( A u. B ) C = ( U_ x e. A C u. U_ x e. B C )
Theorem	iunxprg 3997*	A pair index picks out two instances of an indexed union's argument. (Contributed by Alexander van der Vekens, 2-Feb-2018.)
|- ( x = A -> C = D )   &    |- ( x = B -> C = E )   =>    |- ( ( A e. V /\ B e. W ) -> U_ x e. { A , B } C = ( D u. E ) )
Theorem	iunxiun 3998*	Separate an indexed union in the index of an indexed union. (Contributed by Mario Carneiro, 5-Dec-2016.)
|- U_ x e. U_ y e. A B C = U_ y e. A U_ x e. B C
Theorem	iinuniss 3999*	A relationship involving union and indexed intersection. Exercise 23 of [Enderton] p. 33 but with equality changed to subset. (Contributed by Jim Kingdon, 19-Aug-2018.)
|- ( A u. |^| B ) C_ |^|_ x e. B ( A u. x )
Theorem	iununir 4000*	A relationship involving union and indexed union. Exercise 25 of [Enderton] p. 33 but with biconditional changed to implication. (Contributed by Jim Kingdon, 19-Aug-2018.)
|- ( ( A u. U. B ) = U_ x e. B ( A u. x ) -> ( B = (/) -> A = (/) ) )