P. 57 of Theorem List - Intuitionistic Logic Explorer

Theorem List for Intuitionistic Logic Explorer - 5601-5700   *Has distinct variable group(s)

Type	Label	Description
Statement
Theorem	f1cocnv1 5601	Composition of an injective function with its converse. (Contributed by FL, 11-Nov-2011.)
|- ( F : A -1-1-> B -> ( `' F o. F ) = ( _I |` A ) )
Theorem	funcoeqres 5602	Express a constraint on a composition as a constraint on the composand. (Contributed by Stefan O'Rear, 7-Mar-2015.)
|- ( ( Fun G /\ ( F o. G ) = H ) -> ( F |` ran G ) = ( H o. `' G ) )
Theorem	ffoss 5603*	Relationship between a mapping and an onto mapping. Figure 38 of [Enderton] p. 145. (Contributed by NM, 10-May-1998.)
|- F e. _V   =>    |- ( F : A --> B <-> E. x ( F : A -onto-> x /\ x C_ B ) )
Theorem	f11o 5604*	Relationship between one-to-one and one-to-one onto function. (Contributed by NM, 4-Apr-1998.)
|- F e. _V   =>    |- ( F : A -1-1-> B <-> E. x ( F : A -1-1-onto-> x /\ x C_ B ) )
Theorem	f10 5605	The empty set maps one-to-one into any class. (Contributed by NM, 7-Apr-1998.)
|- (/) : (/) -1-1-> A
Theorem	f10d 5606	The empty set maps one-to-one into any class, deduction version. (Contributed by AV, 25-Nov-2020.)
|- ( ph -> F = (/) )   =>    |- ( ph -> F : dom F -1-1-> A )
Theorem	f1o00 5607	One-to-one onto mapping of the empty set. (Contributed by NM, 15-Apr-1998.)
|- ( F : (/) -1-1-onto-> A <-> ( F = (/) /\ A = (/) ) )
Theorem	fo00 5608	Onto mapping of the empty set. (Contributed by NM, 22-Mar-2006.)
|- ( F : (/) -onto-> A <-> ( F = (/) /\ A = (/) ) )
Theorem	f1o0 5609	One-to-one onto mapping of the empty set. (Contributed by NM, 10-Sep-2004.)
|- (/) : (/) -1-1-onto-> (/)
Theorem	f1oi 5610	A restriction of the identity relation is a one-to-one onto function. (Contributed by NM, 30-Apr-1998.) (Proof shortened by Andrew Salmon, 22-Oct-2011.)
|- ( _I |` A ) : A -1-1-onto-> A
Theorem	f1ovi 5611	The identity relation is a one-to-one onto function on the universe. (Contributed by NM, 16-May-2004.)
|- _I : _V -1-1-onto-> _V
Theorem	f1osn 5612	A singleton of an ordered pair is one-to-one onto function. (Contributed by NM, 18-May-1998.) (Proof shortened by Andrew Salmon, 22-Oct-2011.)
|- A e. _V   &    |- B e. _V   =>    |- { <. A , B >. } : { A } -1-1-onto-> { B }
Theorem	f1osng 5613	A singleton of an ordered pair is one-to-one onto function. (Contributed by Mario Carneiro, 12-Jan-2013.)
|- ( ( A e. V /\ B e. W ) -> { <. A , B >. } : { A } -1-1-onto-> { B } )
Theorem	f1sng 5614	A singleton of an ordered pair is a one-to-one function. (Contributed by AV, 17-Apr-2021.)
|- ( ( A e. V /\ B e. W ) -> { <. A , B >. } : { A } -1-1-> W )
Theorem	fsnd 5615	A singleton of an ordered pair is a function. (Contributed by AV, 17-Apr-2021.)
|- ( ph -> A e. V )   &    |- ( ph -> B e. W )   =>    |- ( ph -> { <. A , B >. } : { A } --> W )
Theorem	f1oprg 5616	An unordered pair of ordered pairs with different elements is a one-to-one onto function. (Contributed by Alexander van der Vekens, 14-Aug-2017.)
|- ( ( ( A e. V /\ B e. W ) /\ ( C e. X /\ D e. Y ) ) -> ( ( A =/= C /\ B =/= D ) -> { <. A , B >. , <. C , D >. } : { A , C } -1-1-onto-> { B , D } ) )
Theorem	tz6.12-2 5617*	Function value when F is not a function. Theorem 6.12(2) of [TakeutiZaring] p. 27. (Contributed by NM, 30-Apr-2004.) (Proof shortened by Mario Carneiro, 31-Aug-2015.)
|- ( -. E! x A F x -> ( F ` A ) = (/) )
Theorem	fveu 5618*	The value of a function at a unique point. (Contributed by Scott Fenton, 6-Oct-2017.)
|- ( E! x A F x -> ( F ` A ) = U. { x | A F x } )
Theorem	brprcneu 5619*	If A is a proper class and F is any class, then there is no unique set which is related to A through the binary relation F. (Contributed by Scott Fenton, 7-Oct-2017.)
|- ( -. A e. _V -> -. E! x A F x )
Theorem	fvprc 5620	A function's value at a proper class is the empty set. (Contributed by NM, 20-May-1998.)
|- ( -. A e. _V -> ( F ` A ) = (/) )
Theorem	fv2 5621*	Alternate definition of function value. Definition 10.11 of [Quine] p. 68. (Contributed by NM, 30-Apr-2004.) (Proof shortened by Andrew Salmon, 17-Sep-2011.) (Revised by Mario Carneiro, 31-Aug-2015.)
|- ( F ` A ) = U. { x | A. y ( A F y <-> y = x ) }
Theorem	dffv3g 5622*	A definition of function value in terms of iota. (Contributed by Jim Kingdon, 29-Dec-2018.)
|- ( A e. V -> ( F ` A ) = ( iota x x e. ( F " { A } ) ) )
Theorem	dffv4g 5623*	The previous definition of function value, from before the iota operator was introduced. Although based on the idea embodied by Definition 10.2 of [Quine] p. 65 (see args 5096), this definition apparently does not appear in the literature. (Contributed by NM, 1-Aug-1994.)
|- ( A e. V -> ( F ` A ) = U. { x | ( F " { A } ) = { x } } )
Theorem	elfv 5624*	Membership in a function value. (Contributed by NM, 30-Apr-2004.)
|- ( A e. ( F ` B ) <-> E. x ( A e. x /\ A. y ( B F y <-> y = x ) ) )
Theorem	fveq1 5625	Equality theorem for function value. (Contributed by NM, 29-Dec-1996.)
|- ( F = G -> ( F ` A ) = ( G ` A ) )
Theorem	fveq2 5626	Equality theorem for function value. (Contributed by NM, 29-Dec-1996.)
|- ( A = B -> ( F ` A ) = ( F ` B ) )
Theorem	fveq1i 5627	Equality inference for function value. (Contributed by NM, 2-Sep-2003.)
|- F = G   =>    |- ( F ` A ) = ( G ` A )
Theorem	fveq1d 5628	Equality deduction for function value. (Contributed by NM, 2-Sep-2003.)
|- ( ph -> F = G )   =>    |- ( ph -> ( F ` A ) = ( G ` A ) )
Theorem	fveq2i 5629	Equality inference for function value. (Contributed by NM, 28-Jul-1999.)
|- A = B   =>    |- ( F ` A ) = ( F ` B )
Theorem	fveq2d 5630	Equality deduction for function value. (Contributed by NM, 29-May-1999.)
|- ( ph -> A = B )   =>    |- ( ph -> ( F ` A ) = ( F ` B ) )
Theorem	2fveq3 5631	Equality theorem for nested function values. (Contributed by AV, 14-Aug-2022.)
|- ( A = B -> ( F ` ( G ` A ) ) = ( F ` ( G ` B ) ) )
Theorem	fveq12i 5632	Equality deduction for function value. (Contributed by FL, 27-Jun-2014.)
|- F = G   &    |- A = B   =>    |- ( F ` A ) = ( G ` B )
Theorem	fveq12d 5633	Equality deduction for function value. (Contributed by FL, 22-Dec-2008.)
|- ( ph -> F = G )   &    |- ( ph -> A = B )   =>    |- ( ph -> ( F ` A ) = ( G ` B ) )
Theorem	fveqeq2d 5634	Equality deduction for function value. (Contributed by BJ, 30-Aug-2022.)
|- ( ph -> A = B )   =>    |- ( ph -> ( ( F ` A ) = C <-> ( F ` B ) = C ) )
Theorem	fveqeq2 5635	Equality deduction for function value. (Contributed by BJ, 31-Aug-2022.)
|- ( A = B -> ( ( F ` A ) = C <-> ( F ` B ) = C ) )
Theorem	nffv 5636	Bound-variable hypothesis builder for function value. (Contributed by NM, 14-Nov-1995.) (Revised by Mario Carneiro, 15-Oct-2016.)
|- F/_ x F   &    |- F/_ x A   =>    |- F/_ x ( F ` A )
Theorem	nffvmpt1 5637*	Bound-variable hypothesis builder for mapping, special case. (Contributed by Mario Carneiro, 25-Dec-2016.)
|- F/_ x ( ( x e. A |-> B ) ` C )
Theorem	nffvd 5638	Deduction version of bound-variable hypothesis builder nffv 5636. (Contributed by NM, 10-Nov-2005.) (Revised by Mario Carneiro, 15-Oct-2016.)
|- ( ph -> F/_ x F )   &    |- ( ph -> F/_ x A )   =>    |- ( ph -> F/_ x ( F ` A ) )
Theorem	funfveu 5639*	A function has one value given an argument in its domain. (Contributed by Jim Kingdon, 29-Dec-2018.)
|- ( ( Fun F /\ A e. dom F ) -> E! y A F y )
Theorem	fvss 5640*	The value of a function is a subset of B if every element that could be a candidate for the value is a subset of B. (Contributed by Mario Carneiro, 24-May-2019.)
|- ( A. x ( A F x -> x C_ B ) -> ( F ` A ) C_ B )
Theorem	fvssunirng 5641	The result of a function value is always a subset of the union of the range, if the input is a set. (Contributed by Stefan O'Rear, 2-Nov-2014.) (Revised by Mario Carneiro, 24-May-2019.)
|- ( A e. _V -> ( F ` A ) C_ U. ran F )
Theorem	relfvssunirn 5642	The result of a function value is always a subset of the union of the range, even if it is invalid and thus empty. (Contributed by Stefan O'Rear, 2-Nov-2014.) (Revised by Mario Carneiro, 24-May-2019.)
|- ( Rel F -> ( F ` A ) C_ U. ran F )
Theorem	funfvex 5643	The value of a function exists. A special case of Corollary 6.13 of [TakeutiZaring] p. 27. (Contributed by Jim Kingdon, 29-Dec-2018.)
|- ( ( Fun F /\ A e. dom F ) -> ( F ` A ) e. _V )
Theorem	relrnfvex 5644	If a function has a set range, then the function value exists unconditional on the domain. (Contributed by Mario Carneiro, 24-May-2019.)
|- ( ( Rel F /\ ran F e. _V ) -> ( F ` A ) e. _V )
Theorem	fvexg 5645	Evaluating a set function at a set exists. (Contributed by Mario Carneiro and Jim Kingdon, 28-May-2019.)
|- ( ( F e. V /\ A e. W ) -> ( F ` A ) e. _V )
Theorem	fvex 5646	Evaluating a set function at a set exists. (Contributed by Mario Carneiro and Jim Kingdon, 28-May-2019.)
|- F e. V   &    |- A e. W   =>    |- ( F ` A ) e. _V
Theorem	sefvex 5647	If a function is set-like, then the function value exists if the input does. (Contributed by Mario Carneiro, 24-May-2019.)
|- ( ( `' F Se _V /\ A e. _V ) -> ( F ` A ) e. _V )
Theorem	fvifdc 5648	Move a conditional outside of a function. (Contributed by Jim Kingdon, 1-Jan-2022.)
|- (DECID ph -> ( F ` if ( ph , A , B ) ) = if ( ph , ( F ` A ) , ( F ` B ) ) )
Theorem	fv3 5649*	Alternate definition of the value of a function. Definition 6.11 of [TakeutiZaring] p. 26. (Contributed by NM, 30-Apr-2004.) (Revised by Mario Carneiro, 31-Aug-2015.)
|- ( F ` A ) = { x | ( E. y ( x e. y /\ A F y ) /\ E! y A F y ) }
Theorem	fvres 5650	The value of a restricted function. (Contributed by NM, 2-Aug-1994.)
|- ( A e. B -> ( ( F |` B ) ` A ) = ( F ` A ) )
Theorem	fvresd 5651	The value of a restricted function, deduction version of fvres 5650. (Contributed by Glauco Siliprandi, 8-Apr-2021.)
|- ( ph -> A e. B )   =>    |- ( ph -> ( ( F |` B ) ` A ) = ( F ` A ) )
Theorem	funssfv 5652	The value of a member of the domain of a subclass of a function. (Contributed by NM, 15-Aug-1994.)
|- ( ( Fun F /\ G C_ F /\ A e. dom G ) -> ( F ` A ) = ( G ` A ) )
Theorem	tz6.12-1 5653*	Function value. Theorem 6.12(1) of [TakeutiZaring] p. 27. (Contributed by NM, 30-Apr-2004.)
|- ( ( A F y /\ E! y A F y ) -> ( F ` A ) = y )
Theorem	tz6.12 5654*	Function value. Theorem 6.12(1) of [TakeutiZaring] p. 27. (Contributed by NM, 10-Jul-1994.)
|- ( ( <. A , y >. e. F /\ E! y <. A , y >. e. F ) -> ( F ` A ) = y )
Theorem	tz6.12f 5655*	Function value, using bound-variable hypotheses instead of distinct variable conditions. (Contributed by NM, 30-Aug-1999.)
|- F/_ y F   =>    |- ( ( <. A , y >. e. F /\ E! y <. A , y >. e. F ) -> ( F ` A ) = y )
Theorem	tz6.12c 5656*	Corollary of Theorem 6.12(1) of [TakeutiZaring] p. 27. (Contributed by NM, 30-Apr-2004.)
|- ( E! y A F y -> ( ( F ` A ) = y <-> A F y ) )
Theorem	ndmfvg 5657	The value of a class outside its domain is the empty set. (Contributed by Jim Kingdon, 15-Jan-2019.)
|- ( ( A e. _V /\ -. A e. dom F ) -> ( F ` A ) = (/) )
Theorem	relelfvdm 5658	If a function value has a member, the argument belongs to the domain. (Contributed by Jim Kingdon, 22-Jan-2019.)
|- ( ( Rel F /\ A e. ( F ` B ) ) -> B e. dom F )
Theorem	elfvm 5659*	If a function value has a member, the function is inhabited. (Contributed by Jim Kingdon, 14-Jun-2025.)
|- ( A e. ( F ` B ) -> E. j j e. F )
Theorem	elfvex 5660	If a function value is inhabited, the function value is a set. (Contributed by Jim Kingdon, 30-Jan-2026.)
|- ( A e. ( F ` B ) -> ( F ` B ) e. _V )
Theorem	fvmbr 5661	If a function value is inhabited, the argument is related to the function value. (Contributed by Jim Kingdon, 31-Jan-2026.)
|- ( A e. ( F ` X ) -> X F ( F ` X ) )
Theorem	nfvres 5662	The value of a non-member of a restriction is the empty set. (Contributed by NM, 13-Nov-1995.)
|- ( -. A e. B -> ( ( F |` B ) ` A ) = (/) )
Theorem	nfunsn 5663	If the restriction of a class to a singleton is not a function, its value is the empty set. (Contributed by NM, 8-Aug-2010.) (Proof shortened by Andrew Salmon, 22-Oct-2011.)
|- ( -. Fun ( F |` { A } ) -> ( F ` A ) = (/) )
Theorem	0fv 5664	Function value of the empty set. (Contributed by Stefan O'Rear, 26-Nov-2014.)
|- ( (/) ` A ) = (/)
Theorem	fv2prc 5665	A function value of a function value at a proper class is the empty set. (Contributed by AV, 8-Apr-2021.)
|- ( -. A e. _V -> ( ( F ` A ) ` B ) = (/) )
Theorem	csbfv12g 5666	Move class substitution in and out of a function value. (Contributed by NM, 11-Nov-2005.)
|- ( A e. C -> [_ A / x ]_ ( F ` B ) = ( [_ A / x ]_ F ` [_ A / x ]_ B ) )
Theorem	csbfv2g 5667*	Move class substitution in and out of a function value. (Contributed by NM, 10-Nov-2005.)
|- ( A e. C -> [_ A / x ]_ ( F ` B ) = ( F ` [_ A / x ]_ B ) )
Theorem	csbfvg 5668*	Substitution for a function value. (Contributed by NM, 1-Jan-2006.)
|- ( A e. C -> [_ A / x ]_ ( F ` x ) = ( F ` A ) )
Theorem	funbrfv 5669	The second argument of a binary relation on a function is the function's value. (Contributed by NM, 30-Apr-2004.) (Revised by Mario Carneiro, 28-Apr-2015.)
|- ( Fun F -> ( A F B -> ( F ` A ) = B ) )
Theorem	funopfv 5670	The second element in an ordered pair member of a function is the function's value. (Contributed by NM, 19-Jul-1996.)
|- ( Fun F -> ( <. A , B >. e. F -> ( F ` A ) = B ) )
Theorem	fnbrfvb 5671	Equivalence of function value and binary relation. (Contributed by NM, 19-Apr-2004.) (Revised by Mario Carneiro, 28-Apr-2015.)
|- ( ( F Fn A /\ B e. A ) -> ( ( F ` B ) = C <-> B F C ) )
Theorem	fnopfvb 5672	Equivalence of function value and ordered pair membership. (Contributed by NM, 7-Nov-1995.)
|- ( ( F Fn A /\ B e. A ) -> ( ( F ` B ) = C <-> <. B , C >. e. F ) )
Theorem	funbrfvb 5673	Equivalence of function value and binary relation. (Contributed by NM, 26-Mar-2006.)
|- ( ( Fun F /\ A e. dom F ) -> ( ( F ` A ) = B <-> A F B ) )
Theorem	funopfvb 5674	Equivalence of function value and ordered pair membership. Theorem 4.3(ii) of [Monk1] p. 42. (Contributed by NM, 26-Jan-1997.)
|- ( ( Fun F /\ A e. dom F ) -> ( ( F ` A ) = B <-> <. A , B >. e. F ) )
Theorem	fnbrfvb2 5675	Version of fnbrfvb 5671 for functions on Cartesian products: function value expressed as a binary relation. See fnbrovb 6045 for the form when F is seen as a binary operation. (Contributed by BJ, 15-Feb-2022.)
|- ( ( F Fn ( V X. W ) /\ ( A e. V /\ B e. W ) ) -> ( ( F ` <. A , B >. ) = C <-> <. A , B >. F C ) )
Theorem	fdmeu 5676*	There is exactly one codomain element for each element of the domain of a function. (Contributed by AV, 20-Apr-2025.)
|- ( ( F : A --> B /\ X e. A ) -> E! y e. B ( F ` X ) = y )
Theorem	funbrfv2b 5677	Function value in terms of a binary relation. (Contributed by Mario Carneiro, 19-Mar-2014.)
|- ( Fun F -> ( A F B <-> ( A e. dom F /\ ( F ` A ) = B ) ) )
Theorem	dffn5im 5678*	Representation of a function in terms of its values. The converse holds given the law of the excluded middle; as it is we have most of the converse via funmpt 5355 and dmmptss 5224. (Contributed by Jim Kingdon, 31-Dec-2018.)
|- ( F Fn A -> F = ( x e. A |-> ( F ` x ) ) )
Theorem	fnrnfv 5679*	The range of a function expressed as a collection of the function's values. (Contributed by NM, 20-Oct-2005.) (Proof shortened by Mario Carneiro, 31-Aug-2015.)
|- ( F Fn A -> ran F = { y | E. x e. A y = ( F ` x ) } )
Theorem	fvelrnb 5680*	A member of a function's range is a value of the function. (Contributed by NM, 31-Oct-1995.)
|- ( F Fn A -> ( B e. ran F <-> E. x e. A ( F ` x ) = B ) )
Theorem	dfimafn 5681*	Alternate definition of the image of a function. (Contributed by Raph Levien, 20-Nov-2006.)
|- ( ( Fun F /\ A C_ dom F ) -> ( F " A ) = { y | E. x e. A ( F ` x ) = y } )
Theorem	dfimafn2 5682*	Alternate definition of the image of a function as an indexed union of singletons of function values. (Contributed by Raph Levien, 20-Nov-2006.)
|- ( ( Fun F /\ A C_ dom F ) -> ( F " A ) = U_ x e. A { ( F ` x ) } )
Theorem	funimass4 5683*	Membership relation for the values of a function whose image is a subclass. (Contributed by Raph Levien, 20-Nov-2006.)
|- ( ( Fun F /\ A C_ dom F ) -> ( ( F " A ) C_ B <-> A. x e. A ( F ` x ) e. B ) )
Theorem	fvelima 5684*	Function value in an image. Part of Theorem 4.4(iii) of [Monk1] p. 42. (Contributed by NM, 29-Apr-2004.) (Proof shortened by Andrew Salmon, 22-Oct-2011.)
|- ( ( Fun F /\ A e. ( F " B ) ) -> E. x e. B ( F ` x ) = A )
Theorem	foelcdmi 5685*	A member of a surjective function's codomain is a value of the function. (Contributed by Thierry Arnoux, 23-Jan-2020.)
|- ( ( F : A -onto-> B /\ Y e. B ) -> E. x e. A ( F ` x ) = Y )
Theorem	feqmptd 5686*	Deduction form of dffn5im 5678. (Contributed by Mario Carneiro, 8-Jan-2015.)
|- ( ph -> F : A --> B )   =>    |- ( ph -> F = ( x e. A |-> ( F ` x ) ) )
Theorem	feqresmpt 5687*	Express a restricted function as a mapping. (Contributed by Mario Carneiro, 18-May-2016.)
|- ( ph -> F : A --> B )   &    |- ( ph -> C C_ A )   =>    |- ( ph -> ( F |` C ) = ( x e. C |-> ( F ` x ) ) )
Theorem	dffn5imf 5688*	Representation of a function in terms of its values. (Contributed by Jim Kingdon, 31-Dec-2018.)
|- F/_ x F   =>    |- ( F Fn A -> F = ( x e. A |-> ( F ` x ) ) )
Theorem	fvelimab 5689*	Function value in an image. (Contributed by NM, 20-Jan-2007.) (Proof shortened by Andrew Salmon, 22-Oct-2011.) (Revised by David Abernethy, 17-Dec-2011.)
|- ( ( F Fn A /\ B C_ A ) -> ( C e. ( F " B ) <-> E. x e. B ( F ` x ) = C ) )
Theorem	fvi 5690	The value of the identity function. (Contributed by NM, 1-May-2004.) (Revised by Mario Carneiro, 28-Apr-2015.)
|- ( A e. V -> ( _I ` A ) = A )
Theorem	fniinfv 5691*	The indexed intersection of a function's values is the intersection of its range. (Contributed by NM, 20-Oct-2005.)
|- ( F Fn A -> |^|_ x e. A ( F ` x ) = |^| ran F )
Theorem	fnsnfv 5692	Singleton of function value. (Contributed by NM, 22-May-1998.)
|- ( ( F Fn A /\ B e. A ) -> { ( F ` B ) } = ( F " { B } ) )
Theorem	fnimapr 5693	The image of a pair under a function. (Contributed by Jeff Madsen, 6-Jan-2011.)
|- ( ( F Fn A /\ B e. A /\ C e. A ) -> ( F " { B , C } ) = { ( F ` B ) , ( F ` C ) } )
Theorem	ssimaex 5694*	The existence of a subimage. (Contributed by NM, 8-Apr-2007.)
|- A e. _V   =>    |- ( ( Fun F /\ B C_ ( F " A ) ) -> E. x ( x C_ A /\ B = ( F " x ) ) )
Theorem	ssimaexg 5695*	The existence of a subimage. (Contributed by FL, 15-Apr-2007.)
|- ( ( A e. C /\ Fun F /\ B C_ ( F " A ) ) -> E. x ( x C_ A /\ B = ( F " x ) ) )
Theorem	funfvdm 5696	A simplified expression for the value of a function when we know it's a function. (Contributed by Jim Kingdon, 1-Jan-2019.)
|- ( ( Fun F /\ A e. dom F ) -> ( F ` A ) = U. ( F " { A } ) )
Theorem	funfvdm2 5697*	The value of a function. Definition of function value in [Enderton] p. 43. (Contributed by Jim Kingdon, 1-Jan-2019.)
|- ( ( Fun F /\ A e. dom F ) -> ( F ` A ) = U. { y | A F y } )
Theorem	funfvdm2f 5698	The value of a function. Version of funfvdm2 5697 using a bound-variable hypotheses instead of distinct variable conditions. (Contributed by Jim Kingdon, 1-Jan-2019.)
|- F/_ y A   &    |- F/_ y F   =>    |- ( ( Fun F /\ A e. dom F ) -> ( F ` A ) = U. { y | A F y } )
Theorem	fvun1 5699	The value of a union when the argument is in the first domain. (Contributed by Scott Fenton, 29-Jun-2013.)
|- ( ( F Fn A /\ G Fn B /\ ( ( A i^i B ) = (/) /\ X e. A ) ) -> ( ( F u. G ) ` X ) = ( F ` X ) )
Theorem	fvun2 5700	The value of a union when the argument is in the second domain. (Contributed by Scott Fenton, 29-Jun-2013.)
|- ( ( F Fn A /\ G Fn B /\ ( ( A i^i B ) = (/) /\ X e. B ) ) -> ( ( F u. G ) ` X ) = ( G ` X ) )