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Theorem List for Intuitionistic Logic Explorer - 5601-5700   *Has distinct variable group(s)
TypeLabelDescription
Statement
 
Theoremisorel 5601 An isomorphism connects binary relations via its function values. (Contributed by NM, 27-Apr-2004.)
 |-  ( ( H  Isom  R ,  S  ( A ,  B )  /\  ( C  e.  A  /\  D  e.  A ) )  ->  ( C R D  <->  ( H `  C ) S ( H `  D ) ) )
 
Theoremisoresbr 5602* A consequence of isomorphism on two relations for a function's restriction. (Contributed by Jim Kingdon, 11-Jan-2019.)
 |-  ( ( F  |`  A ) 
 Isom  R ,  S  ( A ,  ( F
 " A ) ) 
 ->  A. x  e.  A  A. y  e.  A  ( x R y  ->  ( F `  x ) S ( F `  y ) ) )
 
Theoremisoid 5603 Identity law for isomorphism. Proposition 6.30(1) of [TakeutiZaring] p. 33. (Contributed by NM, 27-Apr-2004.)
 |-  (  _I  |`  A ) 
 Isom  R ,  R  ( A ,  A )
 
Theoremisocnv 5604 Converse law for isomorphism. Proposition 6.30(2) of [TakeutiZaring] p. 33. (Contributed by NM, 27-Apr-2004.)
 |-  ( H  Isom  R ,  S  ( A ,  B )  ->  `' H  Isom  S ,  R  ( B ,  A ) )
 
Theoremisocnv2 5605 Converse law for isomorphism. (Contributed by Mario Carneiro, 30-Jan-2014.)
 |-  ( H  Isom  R ,  S  ( A ,  B ) 
 <->  H  Isom  `' R ,  `' S ( A ,  B ) )
 
Theoremisores2 5606 An isomorphism from one well-order to another can be restricted on either well-order. (Contributed by Mario Carneiro, 15-Jan-2013.)
 |-  ( H  Isom  R ,  S  ( A ,  B ) 
 <->  H  Isom  R ,  ( S  i^i  ( B  X.  B ) ) ( A ,  B ) )
 
Theoremisores1 5607 An isomorphism from one well-order to another can be restricted on either well-order. (Contributed by Mario Carneiro, 15-Jan-2013.)
 |-  ( H  Isom  R ,  S  ( A ,  B ) 
 <->  H  Isom  ( R  i^i  ( A  X.  A ) ) ,  S ( A ,  B ) )
 
Theoremisores3 5608 Induced isomorphism on a subset. (Contributed by Stefan O'Rear, 5-Nov-2014.)
 |-  ( ( H  Isom  R ,  S  ( A ,  B )  /\  K  C_  A  /\  X  =  ( H " K ) )  ->  ( H  |`  K )  Isom  R ,  S  ( K ,  X ) )
 
Theoremisotr 5609 Composition (transitive) law for isomorphism. Proposition 6.30(3) of [TakeutiZaring] p. 33. (Contributed by NM, 27-Apr-2004.) (Proof shortened by Mario Carneiro, 5-Dec-2016.)
 |-  ( ( H  Isom  R ,  S  ( A ,  B )  /\  G  Isom  S ,  T  ( B ,  C ) )  ->  ( G  o.  H )  Isom  R ,  T  ( A ,  C ) )
 
Theoremiso0 5610 The empty set is an  R ,  S isomorphism from the empty set to the empty set. (Contributed by Steve Rodriguez, 24-Oct-2015.)
 |-  (/)  Isom  R ,  S  ( (/) ,  (/) )
 
Theoremisoini 5611 Isomorphisms preserve initial segments. Proposition 6.31(2) of [TakeutiZaring] p. 33. (Contributed by NM, 20-Apr-2004.)
 |-  ( ( H  Isom  R ,  S  ( A ,  B )  /\  D  e.  A )  ->  ( H " ( A  i^i  ( `' R " { D } )
 ) )  =  ( B  i^i  ( `' S " { ( H `  D ) }
 ) ) )
 
Theoremisoini2 5612 Isomorphisms are isomorphisms on their initial segments. (Contributed by Mario Carneiro, 29-Mar-2014.)
 |-  C  =  ( A  i^i  ( `' R " { X } )
 )   &    |-  D  =  ( B  i^i  ( `' S " { ( H `  X ) } )
 )   =>    |-  ( ( H  Isom  R ,  S  ( A ,  B )  /\  X  e.  A )  ->  ( H  |`  C ) 
 Isom  R ,  S  ( C ,  D ) )
 
Theoremisoselem 5613* Lemma for isose 5614. (Contributed by Mario Carneiro, 23-Jun-2015.)
 |-  ( ph  ->  H  Isom  R ,  S  ( A ,  B ) )   &    |-  ( ph  ->  ( H " x )  e.  _V )   =>    |-  ( ph  ->  ( R Se  A  ->  S Se  B ) )
 
Theoremisose 5614 An isomorphism preserves set-like relations. (Contributed by Mario Carneiro, 23-Jun-2015.)
 |-  ( H  Isom  R ,  S  ( A ,  B )  ->  ( R Se  A  <->  S Se 
 B ) )
 
Theoremisopolem 5615 Lemma for isopo 5616. (Contributed by Stefan O'Rear, 16-Nov-2014.)
 |-  ( H  Isom  R ,  S  ( A ,  B )  ->  ( S  Po  B  ->  R  Po  A ) )
 
Theoremisopo 5616 An isomorphism preserves partial ordering. (Contributed by Stefan O'Rear, 16-Nov-2014.)
 |-  ( H  Isom  R ,  S  ( A ,  B )  ->  ( R  Po  A 
 <->  S  Po  B ) )
 
Theoremisosolem 5617 Lemma for isoso 5618. (Contributed by Stefan O'Rear, 16-Nov-2014.)
 |-  ( H  Isom  R ,  S  ( A ,  B )  ->  ( S  Or  B  ->  R  Or  A ) )
 
Theoremisoso 5618 An isomorphism preserves strict ordering. (Contributed by Stefan O'Rear, 16-Nov-2014.)
 |-  ( H  Isom  R ,  S  ( A ,  B )  ->  ( R  Or  A 
 <->  S  Or  B ) )
 
Theoremf1oiso 5619* Any one-to-one onto function determines an isomorphism with an induced relation  S. Proposition 6.33 of [TakeutiZaring] p. 34. (Contributed by NM, 30-Apr-2004.)
 |-  ( ( H : A
 -1-1-onto-> B  /\  S  =  { <. z ,  w >.  | 
 E. x  e.  A  E. y  e.  A  ( ( z  =  ( H `  x )  /\  w  =  ( H `  y ) )  /\  x R y ) } )  ->  H  Isom  R ,  S  ( A ,  B ) )
 
Theoremf1oiso2 5620* Any one-to-one onto function determines an isomorphism with an induced relation  S. (Contributed by Mario Carneiro, 9-Mar-2013.)
 |-  S  =  { <. x ,  y >.  |  ( ( x  e.  B  /\  y  e.  B )  /\  ( `' H `  x ) R ( `' H `  y ) ) }   =>    |-  ( H : A -1-1-onto-> B  ->  H  Isom  R ,  S  ( A ,  B ) )
 
2.6.9  Restricted iota (description binder)
 
Syntaxcrio 5621 Extend class notation with restricted description binder.
 class  ( iota_ x  e.  A  ph )
 
Definitiondf-riota 5622 Define restricted description binder. In case there is no unique  x such that  ( x  e.  A  /\  ph ) holds, it evaluates to the empty set. See also comments for df-iota 4993. (Contributed by NM, 15-Sep-2011.) (Revised by Mario Carneiro, 15-Oct-2016.) (Revised by NM, 2-Sep-2018.)
 |-  ( iota_ x  e.  A  ph )  =  ( iota
 x ( x  e.  A  /\  ph )
 )
 
Theoremriotaeqdv 5623* Formula-building deduction for iota. (Contributed by NM, 15-Sep-2011.)
 |-  ( ph  ->  A  =  B )   =>    |-  ( ph  ->  ( iota_ x  e.  A  ps )  =  ( iota_ x  e.  B  ps ) )
 
Theoremriotabidv 5624* Formula-building deduction for restricted iota. (Contributed by NM, 15-Sep-2011.)
 |-  ( ph  ->  ( ps 
 <->  ch ) )   =>    |-  ( ph  ->  (
 iota_ x  e.  A  ps )  =  ( iota_ x  e.  A  ch ) )
 
Theoremriotaeqbidv 5625* Equality deduction for restricted universal quantifier. (Contributed by NM, 15-Sep-2011.)
 |-  ( ph  ->  A  =  B )   &    |-  ( ph  ->  ( ps  <->  ch ) )   =>    |-  ( ph  ->  (
 iota_ x  e.  A  ps )  =  ( iota_ x  e.  B  ch ) )
 
Theoremriotaexg 5626* Restricted iota is a set. (Contributed by Jim Kingdon, 15-Jun-2020.)
 |-  ( A  e.  V  ->  ( iota_ x  e.  A  ps )  e.  _V )
 
Theoremriotav 5627 An iota restricted to the universe is unrestricted. (Contributed by NM, 18-Sep-2011.)
 |-  ( iota_ x  e.  _V  ph )  =  ( iota
 x ph )
 
Theoremriotauni 5628 Restricted iota in terms of class union. (Contributed by NM, 11-Oct-2011.)
 |-  ( E! x  e.  A  ph  ->  ( iota_ x  e.  A  ph )  =  U. { x  e.  A  |  ph } )
 
Theoremnfriota1 5629* The abstraction variable in a restricted iota descriptor isn't free. (Contributed by NM, 12-Oct-2011.) (Revised by Mario Carneiro, 15-Oct-2016.)
 |-  F/_ x ( iota_ x  e.  A  ph )
 
Theoremnfriotadxy 5630* Deduction version of nfriota 5631. (Contributed by Jim Kingdon, 12-Jan-2019.)
 |- 
 F/ y ph   &    |-  ( ph  ->  F/ x ps )   &    |-  ( ph  ->  F/_ x A )   =>    |-  ( ph  ->  F/_ x (
 iota_ y  e.  A  ps ) )
 
Theoremnfriota 5631* A variable not free in a wff remains so in a restricted iota descriptor. (Contributed by NM, 12-Oct-2011.)
 |- 
 F/ x ph   &    |-  F/_ x A   =>    |-  F/_ x ( iota_ y  e.  A  ph )
 
Theoremcbvriota 5632* Change bound variable in a restricted description binder. (Contributed by NM, 18-Mar-2013.) (Revised by Mario Carneiro, 15-Oct-2016.)
 |- 
 F/ y ph   &    |-  F/ x ps   &    |-  ( x  =  y  ->  (
 ph 
 <->  ps ) )   =>    |-  ( iota_ x  e.  A  ph )  =  ( iota_ y  e.  A  ps )
 
Theoremcbvriotav 5633* Change bound variable in a restricted description binder. (Contributed by NM, 18-Mar-2013.) (Revised by Mario Carneiro, 15-Oct-2016.)
 |-  ( x  =  y 
 ->  ( ph  <->  ps ) )   =>    |-  ( iota_ x  e.  A  ph )  =  ( iota_ y  e.  A  ps )
 
Theoremcsbriotag 5634* Interchange class substitution and restricted description binder. (Contributed by NM, 24-Feb-2013.)
 |-  ( A  e.  V  -> 
 [_ A  /  x ]_ ( iota_ y  e.  B  ph )  =  ( iota_ y  e.  B  [. A  /  x ]. ph )
 )
 
Theoremriotacl2 5635 Membership law for "the unique element in  A such that  ph."

(Contributed by NM, 21-Aug-2011.) (Revised by Mario Carneiro, 23-Dec-2016.)

 |-  ( E! x  e.  A  ph  ->  ( iota_ x  e.  A  ph )  e.  { x  e.  A  |  ph } )
 
Theoremriotacl 5636* Closure of restricted iota. (Contributed by NM, 21-Aug-2011.)
 |-  ( E! x  e.  A  ph  ->  ( iota_ x  e.  A  ph )  e.  A )
 
Theoremriotasbc 5637 Substitution law for descriptions. (Contributed by NM, 23-Aug-2011.) (Proof shortened by Mario Carneiro, 24-Dec-2016.)
 |-  ( E! x  e.  A  ph  ->  [. ( iota_ x  e.  A  ph )  /  x ]. ph )
 
Theoremriotabidva 5638* Equivalent wff's yield equal restricted class abstractions (deduction form). (rabbidva 2608 analog.) (Contributed by NM, 17-Jan-2012.)
 |-  ( ( ph  /\  x  e.  A )  ->  ( ps 
 <->  ch ) )   =>    |-  ( ph  ->  (
 iota_ x  e.  A  ps )  =  ( iota_ x  e.  A  ch ) )
 
Theoremriotabiia 5639 Equivalent wff's yield equal restricted iotas (inference form). (rabbiia 2605 analog.) (Contributed by NM, 16-Jan-2012.)
 |-  ( x  e.  A  ->  ( ph  <->  ps ) )   =>    |-  ( iota_ x  e.  A  ph )  =  ( iota_ x  e.  A  ps )
 
Theoremriota1 5640* Property of restricted iota. Compare iota1 5007. (Contributed by Mario Carneiro, 15-Oct-2016.)
 |-  ( E! x  e.  A  ph  ->  ( ( x  e.  A  /\  ph )  <->  ( iota_ x  e.  A  ph )  =  x ) )
 
Theoremriota1a 5641 Property of iota. (Contributed by NM, 23-Aug-2011.)
 |-  ( ( x  e.  A  /\  E! x  e.  A  ph )  ->  ( ph  <->  ( iota x ( x  e.  A  /\  ph ) )  =  x ) )
 
Theoremriota2df 5642* A deduction version of riota2f 5643. (Contributed by NM, 17-Feb-2013.) (Revised by Mario Carneiro, 15-Oct-2016.)
 |- 
 F/ x ph   &    |-  ( ph  ->  F/_ x B )   &    |-  ( ph  ->  F/ x ch )   &    |-  ( ph  ->  B  e.  A )   &    |-  ( ( ph  /\  x  =  B ) 
 ->  ( ps  <->  ch ) )   =>    |-  ( ( ph  /\ 
 E! x  e.  A  ps )  ->  ( ch  <->  (
 iota_ x  e.  A  ps )  =  B ) )
 
Theoremriota2f 5643* This theorem shows a condition that allows us to represent a descriptor with a class expression  B. (Contributed by NM, 23-Aug-2011.) (Revised by Mario Carneiro, 15-Oct-2016.)
 |-  F/_ x B   &    |-  F/ x ps   &    |-  ( x  =  B  ->  (
 ph 
 <->  ps ) )   =>    |-  ( ( B  e.  A  /\  E! x  e.  A  ph )  ->  ( ps  <->  ( iota_ x  e.  A  ph )  =  B ) )
 
Theoremriota2 5644* This theorem shows a condition that allows us to represent a descriptor with a class expression  B. (Contributed by NM, 23-Aug-2011.) (Revised by Mario Carneiro, 10-Dec-2016.)
 |-  ( x  =  B  ->  ( ph  <->  ps ) )   =>    |-  ( ( B  e.  A  /\  E! x  e.  A  ph )  ->  ( ps  <->  ( iota_ x  e.  A  ph )  =  B ) )
 
Theoremriotaprop 5645* Properties of a restricted definite description operator. Todo (df-riota 5622 update): can some uses of riota2f 5643 be shortened with this? (Contributed by NM, 23-Nov-2013.)
 |- 
 F/ x ps   &    |-  B  =  ( iota_ x  e.  A  ph )   &    |-  ( x  =  B  ->  ( ph  <->  ps ) )   =>    |-  ( E! x  e.  A  ph  ->  ( B  e.  A  /\  ps ) )
 
Theoremriota5f 5646* A method for computing restricted iota. (Contributed by NM, 16-Apr-2013.) (Revised by Mario Carneiro, 15-Oct-2016.)
 |-  ( ph  ->  F/_ x B )   &    |-  ( ph  ->  B  e.  A )   &    |-  (
 ( ph  /\  x  e.  A )  ->  ( ps 
 <->  x  =  B ) )   =>    |-  ( ph  ->  ( iota_ x  e.  A  ps )  =  B )
 
Theoremriota5 5647* A method for computing restricted iota. (Contributed by NM, 20-Oct-2011.) (Revised by Mario Carneiro, 6-Dec-2016.)
 |-  ( ph  ->  B  e.  A )   &    |-  ( ( ph  /\  x  e.  A ) 
 ->  ( ps  <->  x  =  B ) )   =>    |-  ( ph  ->  ( iota_ x  e.  A  ps )  =  B )
 
Theoremriotass2 5648* Restriction of a unique element to a smaller class. (Contributed by NM, 21-Aug-2011.) (Revised by NM, 22-Mar-2013.)
 |-  ( ( ( A 
 C_  B  /\  A. x  e.  A  ( ph  ->  ps ) )  /\  ( E. x  e.  A  ph 
 /\  E! x  e.  B  ps ) )  ->  ( iota_ x  e.  A  ph )  =  ( iota_ x  e.  B  ps ) )
 
Theoremriotass 5649* Restriction of a unique element to a smaller class. (Contributed by NM, 19-Oct-2005.) (Revised by Mario Carneiro, 24-Dec-2016.)
 |-  ( ( A  C_  B  /\  E. x  e.  A  ph  /\  E! x  e.  B  ph )  ->  ( iota_ x  e.  A  ph )  =  ( iota_ x  e.  B  ph )
 )
 
Theoremmoriotass 5650* Restriction of a unique element to a smaller class. (Contributed by NM, 19-Feb-2006.) (Revised by NM, 16-Jun-2017.)
 |-  ( ( A  C_  B  /\  E. x  e.  A  ph  /\  E* x  e.  B  ph )  ->  ( iota_ x  e.  A  ph )  =  ( iota_ x  e.  B  ph )
 )
 
Theoremsnriota 5651 A restricted class abstraction with a unique member can be expressed as a singleton. (Contributed by NM, 30-May-2006.)
 |-  ( E! x  e.  A  ph  ->  { x  e.  A  |  ph }  =  { ( iota_ x  e.  A  ph ) }
 )
 
Theoremeusvobj2 5652* Specify the same property in two ways when class  B ( y ) is single-valued. (Contributed by NM, 1-Nov-2010.) (Proof shortened by Mario Carneiro, 24-Dec-2016.)
 |-  B  e.  _V   =>    |-  ( E! x E. y  e.  A  x  =  B  ->  ( E. y  e.  A  x  =  B  <->  A. y  e.  A  x  =  B )
 )
 
Theoremeusvobj1 5653* Specify the same object in two ways when class  B ( y ) is single-valued. (Contributed by NM, 1-Nov-2010.) (Proof shortened by Mario Carneiro, 19-Nov-2016.)
 |-  B  e.  _V   =>    |-  ( E! x E. y  e.  A  x  =  B  ->  (
 iota x E. y  e.  A  x  =  B )  =  ( iota x
 A. y  e.  A  x  =  B )
 )
 
Theoremf1ofveu 5654* There is one domain element for each value of a one-to-one onto function. (Contributed by NM, 26-May-2006.)
 |-  ( ( F : A
 -1-1-onto-> B  /\  C  e.  B )  ->  E! x  e.  A  ( F `  x )  =  C )
 
Theoremf1ocnvfv3 5655* Value of the converse of a one-to-one onto function. (Contributed by NM, 26-May-2006.) (Proof shortened by Mario Carneiro, 24-Dec-2016.)
 |-  ( ( F : A
 -1-1-onto-> B  /\  C  e.  B )  ->  ( `' F `  C )  =  (
 iota_ x  e.  A  ( F `  x )  =  C ) )
 
Theoremriotaund 5656* Restricted iota equals the empty set when not meaningful. (Contributed by NM, 16-Jan-2012.) (Revised by Mario Carneiro, 15-Oct-2016.) (Revised by NM, 13-Sep-2018.)
 |-  ( -.  E! x  e.  A  ph  ->  ( iota_ x  e.  A  ph )  =  (/) )
 
Theoremacexmidlema 5657* Lemma for acexmid 5665. (Contributed by Jim Kingdon, 6-Aug-2019.)
 |-  A  =  { x  e.  { (/) ,  { (/) } }  |  ( x  =  (/)  \/  ph ) }   &    |-  B  =  { x  e.  { (/) ,  { (/)
 } }  |  ( x  =  { (/) }  \/  ph ) }   &    |-  C  =  { A ,  B }   =>    |-  ( { (/) }  e.  A  -> 
 ph )
 
Theoremacexmidlemb 5658* Lemma for acexmid 5665. (Contributed by Jim Kingdon, 6-Aug-2019.)
 |-  A  =  { x  e.  { (/) ,  { (/) } }  |  ( x  =  (/)  \/  ph ) }   &    |-  B  =  { x  e.  { (/) ,  { (/)
 } }  |  ( x  =  { (/) }  \/  ph ) }   &    |-  C  =  { A ,  B }   =>    |-  ( (/) 
 e.  B  ->  ph )
 
Theoremacexmidlemph 5659* Lemma for acexmid 5665. (Contributed by Jim Kingdon, 6-Aug-2019.)
 |-  A  =  { x  e.  { (/) ,  { (/) } }  |  ( x  =  (/)  \/  ph ) }   &    |-  B  =  { x  e.  { (/) ,  { (/)
 } }  |  ( x  =  { (/) }  \/  ph ) }   &    |-  C  =  { A ,  B }   =>    |-  ( ph  ->  A  =  B )
 
Theoremacexmidlemab 5660* Lemma for acexmid 5665. (Contributed by Jim Kingdon, 6-Aug-2019.)
 |-  A  =  { x  e.  { (/) ,  { (/) } }  |  ( x  =  (/)  \/  ph ) }   &    |-  B  =  { x  e.  { (/) ,  { (/)
 } }  |  ( x  =  { (/) }  \/  ph ) }   &    |-  C  =  { A ,  B }   =>    |-  (
 ( ( iota_ v  e.  A  E. u  e.  y  ( A  e.  u  /\  v  e.  u ) )  =  (/)  /\  ( iota_
 v  e.  B  E. u  e.  y  ( B  e.  u  /\  v  e.  u )
 )  =  { (/) } )  ->  -.  ph )
 
Theoremacexmidlemcase 5661* Lemma for acexmid 5665. Here we divide the proof into cases (based on the disjunction implicit in an unordered pair, not the sort of case elimination which relies on excluded middle).

The cases are (1) the choice function evaluated at  A equals  { (/) }, (2) the choice function evaluated at  B equals  (/), and (3) the choice function evaluated at  A equals 
(/) and the choice function evaluated at  B equals  { (/) }.

Because of the way we represent the choice function  y, the choice function evaluated at  A is  ( iota_ v  e.  A E. u  e.  y ( A  e.  u  /\  v  e.  u ) ) and the choice function evaluated at  B is  ( iota_ v  e.  B E. u  e.  y ( B  e.  u  /\  v  e.  u ) ). Other than the difference in notation these work just as  ( y `  A ) and  ( y `  B ) would if  y were a function as defined by df-fun 5030.

Although it isn't exactly about the division into cases, it is also convenient for this lemma to also include the step that if the choice function evaluated at  A equals  { (/) }, then  { (/) }  e.  A and likewise for  B.

(Contributed by Jim Kingdon, 7-Aug-2019.)

 |-  A  =  { x  e.  { (/) ,  { (/) } }  |  ( x  =  (/)  \/  ph ) }   &    |-  B  =  { x  e.  { (/) ,  { (/)
 } }  |  ( x  =  { (/) }  \/  ph ) }   &    |-  C  =  { A ,  B }   =>    |-  ( A. z  e.  C  E! v  e.  z  E. u  e.  y  ( z  e.  u  /\  v  e.  u )  ->  ( { (/) }  e.  A  \/  (/)  e.  B  \/  ( ( iota_ v  e.  A  E. u  e.  y  ( A  e.  u  /\  v  e.  u ) )  =  (/)  /\  ( iota_
 v  e.  B  E. u  e.  y  ( B  e.  u  /\  v  e.  u )
 )  =  { (/) } )
 ) )
 
Theoremacexmidlem1 5662* Lemma for acexmid 5665. List the cases identified in acexmidlemcase 5661 and hook them up to the lemmas which handle each case. (Contributed by Jim Kingdon, 7-Aug-2019.)
 |-  A  =  { x  e.  { (/) ,  { (/) } }  |  ( x  =  (/)  \/  ph ) }   &    |-  B  =  { x  e.  { (/) ,  { (/)
 } }  |  ( x  =  { (/) }  \/  ph ) }   &    |-  C  =  { A ,  B }   =>    |-  ( A. z  e.  C  E! v  e.  z  E. u  e.  y  ( z  e.  u  /\  v  e.  u )  ->  ( ph  \/  -.  ph ) )
 
Theoremacexmidlem2 5663* Lemma for acexmid 5665. This builds on acexmidlem1 5662 by noting that every element of  C is inhabited.

(Note that  y is not quite a function in the df-fun 5030 sense because it uses ordered pairs as described in opthreg 4385 rather than df-op 3459).

The set  A is also found in onsucelsucexmidlem 4358.

(Contributed by Jim Kingdon, 5-Aug-2019.)

 |-  A  =  { x  e.  { (/) ,  { (/) } }  |  ( x  =  (/)  \/  ph ) }   &    |-  B  =  { x  e.  { (/) ,  { (/)
 } }  |  ( x  =  { (/) }  \/  ph ) }   &    |-  C  =  { A ,  B }   =>    |-  ( A. z  e.  C  A. w  e.  z  E! v  e.  z  E. u  e.  y  (
 z  e.  u  /\  v  e.  u )  ->  ( ph  \/  -.  ph ) )
 
Theoremacexmidlemv 5664* Lemma for acexmid 5665.

This is acexmid 5665 with additional distinct variable constraints, most notably between  ph and  x.

(Contributed by Jim Kingdon, 6-Aug-2019.)

 |- 
 E. y A. z  e.  x  A. w  e.  z  E! v  e.  z  E. u  e.  y  ( z  e.  u  /\  v  e.  u )   =>    |-  ( ph  \/  -.  ph )
 
Theoremacexmid 5665* The axiom of choice implies excluded middle. Theorem 1.3 in [Bauer] p. 483.

The statement of the axiom of choice given here is ac2 in the Metamath Proof Explorer (version of 3-Aug-2019). In particular, note that the choice function  y provides a value when  z is inhabited (as opposed to nonempty as in some statements of the axiom of choice).

Essentially the same proof can also be found at "The axiom of choice implies instances of EM", [Crosilla], p. "Set-theoretic principles incompatible with intuitionistic logic".

Often referred to as Diaconescu's theorem, or Diaconescu-Goodman-Myhill theorem, after Radu Diaconescu who discovered it in 1975 in the framework of topos theory and N. D. Goodman and John Myhill in 1978 in the framework of set theory (although it already appeared as an exercise in Errett Bishop's book Foundations of Constructive Analysis from 1967).

(Contributed by Jim Kingdon, 4-Aug-2019.)

 |- 
 E. y A. z  e.  x  A. w  e.  z  E! v  e.  z  E. u  e.  y  ( z  e.  u  /\  v  e.  u )   =>    |-  ( ph  \/  -.  ph )
 
2.6.10  Operations
 
Syntaxco 5666 Extend class notation to include the value of an operation  F (such as + ) for two arguments  A and  B. Note that the syntax is simply three class symbols in a row surrounded by parentheses. Since operation values are the only possible class expressions consisting of three class expressions in a row surrounded by parentheses, the syntax is unambiguous.
 class  ( A F B )
 
Syntaxcoprab 5667 Extend class notation to include class abstraction (class builder) of nested ordered pairs.
 class  { <. <. x ,  y >. ,  z >.  |  ph }
 
Syntaxcmpt2 5668 Extend the definition of a class to include maps-to notation for defining an operation via a rule.
 class  ( x  e.  A ,  y  e.  B  |->  C )
 
Definitiondf-ov 5669 Define the value of an operation. Definition of operation value in [Enderton] p. 79. Note that the syntax is simply three class expressions in a row bracketed by parentheses. There are no restrictions of any kind on what those class expressions may be, although only certain kinds of class expressions - a binary operation  F and its arguments  A and  B- will be useful for proving meaningful theorems. For example, if class  F is the operation + and arguments  A and  B are 3 and 2 , the expression ( 3 + 2 ) can be proved to equal 5 . This definition is well-defined, although not very meaningful, when classes  A and/or  B are proper classes (i.e. are not sets); see ovprc1 5699 and ovprc2 5700. On the other hand, we often find uses for this definition when  F is a proper class.  F is normally equal to a class of nested ordered pairs of the form defined by df-oprab 5670. (Contributed by NM, 28-Feb-1995.)
 |-  ( A F B )  =  ( F ` 
 <. A ,  B >. )
 
Definitiondf-oprab 5670* Define the class abstraction (class builder) of a collection of nested ordered pairs (for use in defining operations). This is a special case of Definition 4.16 of [TakeutiZaring] p. 14. Normally  x,  y, and  z are distinct, although the definition doesn't strictly require it. See df-ov 5669 for the value of an operation. The brace notation is called "class abstraction" by Quine; it is also called a "class builder" in the literature. The value of the most common operation class builder is given by ovmpt2 5794. (Contributed by NM, 12-Mar-1995.)
 |- 
 { <. <. x ,  y >. ,  z >.  |  ph }  =  { w  |  E. x E. y E. z ( w  = 
 <. <. x ,  y >. ,  z >.  /\  ph ) }
 
Definitiondf-mpt2 5671* Define maps-to notation for defining an operation via a rule. Read as "the operation defined by the map from  x ,  y (in  A  X.  B) to  B ( x ,  y )." An extension of df-mpt 3907 for two arguments. (Contributed by NM, 17-Feb-2008.)
 |-  ( x  e.  A ,  y  e.  B  |->  C )  =  { <.
 <. x ,  y >. ,  z >.  |  (
 ( x  e.  A  /\  y  e.  B )  /\  z  =  C ) }
 
Theoremoveq 5672 Equality theorem for operation value. (Contributed by NM, 28-Feb-1995.)
 |-  ( F  =  G  ->  ( A F B )  =  ( A G B ) )
 
Theoremoveq1 5673 Equality theorem for operation value. (Contributed by NM, 28-Feb-1995.)
 |-  ( A  =  B  ->  ( A F C )  =  ( B F C ) )
 
Theoremoveq2 5674 Equality theorem for operation value. (Contributed by NM, 28-Feb-1995.)
 |-  ( A  =  B  ->  ( C F A )  =  ( C F B ) )
 
Theoremoveq12 5675 Equality theorem for operation value. (Contributed by NM, 16-Jul-1995.)
 |-  ( ( A  =  B  /\  C  =  D )  ->  ( A F C )  =  ( B F D ) )
 
Theoremoveq1i 5676 Equality inference for operation value. (Contributed by NM, 28-Feb-1995.)
 |-  A  =  B   =>    |-  ( A F C )  =  ( B F C )
 
Theoremoveq2i 5677 Equality inference for operation value. (Contributed by NM, 28-Feb-1995.)
 |-  A  =  B   =>    |-  ( C F A )  =  ( C F B )
 
Theoremoveq12i 5678 Equality inference for operation value. (Contributed by NM, 28-Feb-1995.) (Proof shortened by Andrew Salmon, 22-Oct-2011.)
 |-  A  =  B   &    |-  C  =  D   =>    |-  ( A F C )  =  ( B F D )
 
Theoremoveqi 5679 Equality inference for operation value. (Contributed by NM, 24-Nov-2007.)
 |-  A  =  B   =>    |-  ( C A D )  =  ( C B D )
 
Theoremoveq123i 5680 Equality inference for operation value. (Contributed by FL, 11-Jul-2010.)
 |-  A  =  C   &    |-  B  =  D   &    |-  F  =  G   =>    |-  ( A F B )  =  ( C G D )
 
Theoremoveq1d 5681 Equality deduction for operation value. (Contributed by NM, 13-Mar-1995.)
 |-  ( ph  ->  A  =  B )   =>    |-  ( ph  ->  ( A F C )  =  ( B F C ) )
 
Theoremoveq2d 5682 Equality deduction for operation value. (Contributed by NM, 13-Mar-1995.)
 |-  ( ph  ->  A  =  B )   =>    |-  ( ph  ->  ( C F A )  =  ( C F B ) )
 
Theoremoveqd 5683 Equality deduction for operation value. (Contributed by NM, 9-Sep-2006.)
 |-  ( ph  ->  A  =  B )   =>    |-  ( ph  ->  ( C A D )  =  ( C B D ) )
 
Theoremoveq12d 5684 Equality deduction for operation value. (Contributed by NM, 13-Mar-1995.) (Proof shortened by Andrew Salmon, 22-Oct-2011.)
 |-  ( ph  ->  A  =  B )   &    |-  ( ph  ->  C  =  D )   =>    |-  ( ph  ->  ( A F C )  =  ( B F D ) )
 
Theoremoveqan12d 5685 Equality deduction for operation value. (Contributed by NM, 10-Aug-1995.)
 |-  ( ph  ->  A  =  B )   &    |-  ( ps  ->  C  =  D )   =>    |-  ( ( ph  /\ 
 ps )  ->  ( A F C )  =  ( B F D ) )
 
Theoremoveqan12rd 5686 Equality deduction for operation value. (Contributed by NM, 10-Aug-1995.)
 |-  ( ph  ->  A  =  B )   &    |-  ( ps  ->  C  =  D )   =>    |-  ( ( ps 
 /\  ph )  ->  ( A F C )  =  ( B F D ) )
 
Theoremoveq123d 5687 Equality deduction for operation value. (Contributed by FL, 22-Dec-2008.)
 |-  ( ph  ->  F  =  G )   &    |-  ( ph  ->  A  =  B )   &    |-  ( ph  ->  C  =  D )   =>    |-  ( ph  ->  ( A F C )  =  ( B G D ) )
 
Theoremfvoveq1d 5688 Equality deduction for nested function and operation value. (Contributed by AV, 23-Jul-2022.)
 |-  ( ph  ->  A  =  B )   =>    |-  ( ph  ->  ( F `  ( A O C ) )  =  ( F `  ( B O C ) ) )
 
Theoremfvoveq1 5689 Equality theorem for nested function and operation value. Closed form of fvoveq1d 5688. (Contributed by AV, 23-Jul-2022.)
 |-  ( A  =  B  ->  ( F `  ( A O C ) )  =  ( F `  ( B O C ) ) )
 
Theoremovanraleqv 5690* Equality theorem for a conjunction with an operation values within a restricted universal quantification. Technical theorem to be used to reduce the size of a significant number of proofs. (Contributed by AV, 13-Aug-2022.)
 |-  ( B  =  X  ->  ( ph  <->  ps ) )   =>    |-  ( B  =  X  ->  ( A. x  e.  V  ( ph  /\  ( A  .x.  B )  =  C )  <->  A. x  e.  V  ( ps  /\  ( A 
 .x.  X )  =  C ) ) )
 
Theoremimbrov2fvoveq 5691 Equality theorem for nested function and operation value in an implication for a binary relation. Technical theorem to be used to reduce the size of a significant number of proofs. (Contributed by AV, 17-Aug-2022.)
 |-  ( X  =  Y  ->  ( ph  <->  ps ) )   =>    |-  ( X  =  Y  ->  ( ( ph  ->  ( F `  (
 ( G `  X )  .x.  O ) ) R A )  <->  ( ps  ->  ( F `  ( ( G `  Y ) 
 .x.  O ) ) R A ) ) )
 
Theoremnfovd 5692 Deduction version of bound-variable hypothesis builder nfov 5693. (Contributed by NM, 13-Dec-2005.) (Proof shortened by Andrew Salmon, 22-Oct-2011.)
 |-  ( ph  ->  F/_ x A )   &    |-  ( ph  ->  F/_ x F )   &    |-  ( ph  ->  F/_ x B )   =>    |-  ( ph  ->  F/_ x ( A F B ) )
 
Theoremnfov 5693 Bound-variable hypothesis builder for operation value. (Contributed by NM, 4-May-2004.)
 |-  F/_ x A   &    |-  F/_ x F   &    |-  F/_ x B   =>    |-  F/_ x ( A F B )
 
Theoremoprabidlem 5694* Slight elaboration of exdistrfor 1729. A lemma for oprabid 5695. (Contributed by Jim Kingdon, 15-Jan-2019.)
 |-  ( E. x E. y ( x  =  z  /\  ps )  ->  E. x ( x  =  z  /\  E. y ps ) )
 
Theoremoprabid 5695 The law of concretion. Special case of Theorem 9.5 of [Quine] p. 61. Although this theorem would be useful with a distinct variable constraint between  x,  y, and  z, we use ax-bndl 1445 to eliminate that constraint. (Contributed by Mario Carneiro, 20-Mar-2013.)
 |-  ( <. <. x ,  y >. ,  z >.  e.  { <.
 <. x ,  y >. ,  z >.  |  ph }  <->  ph )
 
Theoremfnovex 5696 The result of an operation is a set. (Contributed by Jim Kingdon, 15-Jan-2019.)
 |-  ( ( F  Fn  ( C  X.  D ) 
 /\  A  e.  C  /\  B  e.  D ) 
 ->  ( A F B )  e.  _V )
 
Theoremovexg 5697 Evaluating a set operation at two sets gives a set. (Contributed by Jim Kingdon, 19-Aug-2021.)
 |-  ( ( A  e.  V  /\  F  e.  W  /\  B  e.  X ) 
 ->  ( A F B )  e.  _V )
 
Theoremovprc 5698 The value of an operation when the one of the arguments is a proper class. Note: this theorem is dependent on our particular definitions of operation value, function value, and ordered pair. (Contributed by Mario Carneiro, 26-Apr-2015.)
 |- 
 Rel  dom  F   =>    |-  ( -.  ( A  e.  _V  /\  B  e.  _V )  ->  ( A F B )  =  (/) )
 
Theoremovprc1 5699 The value of an operation when the first argument is a proper class. (Contributed by NM, 16-Jun-2004.)
 |- 
 Rel  dom  F   =>    |-  ( -.  A  e.  _V 
 ->  ( A F B )  =  (/) )
 
Theoremovprc2 5700 The value of an operation when the second argument is a proper class. (Contributed by Mario Carneiro, 26-Apr-2015.)
 |- 
 Rel  dom  F   =>    |-  ( -.  B  e.  _V 
 ->  ( A F B )  =  (/) )
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