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Theorem List for Intuitionistic Logic Explorer - 7001-7100   *Has distinct variable group(s)
TypeLabelDescription
Statement
 
Theoremsupelti 7001* 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 )
 
Theoremsup00 7002 The supremum under an empty base set is always the empty set. (Contributed by AV, 4-Sep-2020.)
 |- 
 sup ( B ,  (/)
 ,  R )  =  (/)
 
Theoremsupmaxti 7003* 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 )
 
Theoremsupsnti 7004* 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 )
 
Theoremisotilem 7005* Lemma for isoti 7006. (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 ) ) ) )
 
Theoremisoti 7006* 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 ) ) ) )
 
Theoremsupisolem 7007* Lemma for supisoti 7009. (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 ) ) ) )
 
Theoremsupisoex 7008* Lemma for supisoti 7009. (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 ) ) )
 
Theoremsupisoti 7009* 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 )
 ) )
 
Theoreminfeq1 7010 Equality theorem for infimum. (Contributed by AV, 2-Sep-2020.)
 |-  ( B  =  C  -> inf ( B ,  A ,  R )  = inf ( C ,  A ,  R ) )
 
Theoreminfeq1d 7011 Equality deduction for infimum. (Contributed by AV, 2-Sep-2020.)
 |-  ( ph  ->  B  =  C )   =>    |-  ( ph  -> inf ( B ,  A ,  R )  = inf ( C ,  A ,  R ) )
 
Theoreminfeq1i 7012 Equality inference for infimum. (Contributed by AV, 2-Sep-2020.)
 |-  B  =  C   =>    |- inf ( B ,  A ,  R )  = inf ( C ,  A ,  R )
 
Theoreminfeq2 7013 Equality theorem for infimum. (Contributed by AV, 2-Sep-2020.)
 |-  ( B  =  C  -> inf ( A ,  B ,  R )  = inf ( A ,  C ,  R ) )
 
Theoreminfeq3 7014 Equality theorem for infimum. (Contributed by AV, 2-Sep-2020.)
 |-  ( R  =  S  -> inf ( A ,  B ,  R )  = inf ( A ,  B ,  S ) )
 
Theoreminfeq123d 7015 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 ) )
 
Theoremnfinf 7016 Hypothesis builder for infimum. (Contributed by AV, 2-Sep-2020.)
 |-  F/_ x A   &    |-  F/_ x B   &    |-  F/_ x R   =>    |-  F/_ xinf ( A ,  B ,  R )
 
Theoremcnvinfex 7017* 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 ) ) )
 
Theoremcnvti 7018* 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 ) ) )
 
Theoremeqinfti 7019* 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 )
 )
 
Theoremeqinftid 7020* 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 )
 
Theoreminfvalti 7021* 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 ) ) ) )
 
Theoreminfclti 7022* An infimum belongs to its base class (closure law). See also inflbti 7023 and infglbti 7024. (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 )
 
Theoreminflbti 7023* An infimum is a lower bound. See also infclti 7022 and infglbti 7024. (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 ) ) )
 
Theoreminfglbti 7024* An infimum is the greatest lower bound. See also infclti 7022 and inflbti 7023. (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 ) )
 
Theoreminfnlbti 7025* 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 ) )
 
Theoreminfminti 7026* 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 )
 
Theoreminfmoti 7027* 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 ) ) )
 
Theoreminfeuti 7028* 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 ) ) )
 
Theoreminfsnti 7029* 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 )
 
Theoreminf00 7030 The infimum regarding an empty base set is always the empty set. (Contributed by AV, 4-Sep-2020.)
 |- inf
 ( B ,  (/) ,  R )  =  (/)
 
Theoreminfisoti 7031* 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 ) ) )
 
Theoremsupex2g 7032 Existence of supremum. (Contributed by Jeff Madsen, 2-Sep-2009.)
 |-  ( A  e.  C  ->  sup ( B ,  A ,  R )  e.  _V )
 
Theoreminfex2g 7033 Existence of infimum. (Contributed by Jim Kingdon, 1-Oct-2024.)
 |-  ( A  e.  C  -> inf ( B ,  A ,  R )  e.  _V )
 
2.6.35  Ordinal isomorphism
 
Theoremordiso2 7034 Generalize ordiso 7035 to proper classes. (Contributed by Mario Carneiro, 24-Jun-2015.)
 |-  ( ( F  Isom  _E 
 ,  _E  ( A ,  B )  /\  Ord 
 A  /\  Ord  B ) 
 ->  A  =  B )
 
Theoremordiso 7035* 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 ) ) )
 
2.6.36  Disjoint union
 
2.6.36.1  Disjoint union
 
Syntaxcdju 7036 Extend class notation to include disjoint union of two classes.
 class  ( A B )
 
Definitiondf-dju 7037 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 ) )
 
Theoremdjueq12 7038 Equality theorem for disjoint union. (Contributed by Jim Kingdon, 23-Jun-2022.)
 |-  ( ( A  =  B  /\  C  =  D )  ->  ( A C )  =  ( B D ) )
 
Theoremdjueq1 7039 Equality theorem for disjoint union. (Contributed by Jim Kingdon, 23-Jun-2022.)
 |-  ( A  =  B  ->  ( A C )  =  ( B C )
 )
 
Theoremdjueq2 7040 Equality theorem for disjoint union. (Contributed by Jim Kingdon, 23-Jun-2022.)
 |-  ( A  =  B  ->  ( C A )  =  ( C B )
 )
 
Theoremnfdju 7041 Bound-variable hypothesis builder for disjoint union. (Contributed by Jim Kingdon, 23-Jun-2022.)
 |-  F/_ x A   &    |-  F/_ x B   =>    |-  F/_ x ( A B )
 
Theoremdjuex 7042 The disjoint union of sets is a set. See also the more precise djuss 7069. (Contributed by AV, 28-Jun-2022.)
 |-  ( ( A  e.  V  /\  B  e.  W )  ->  ( A B )  e.  _V )
 
Theoremdjuexb 7043 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 )
 
2.6.36.2  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 ).

 
Syntaxcinl 7044 Extend class notation to include left injection of a disjoint union.
 class inl
 
Syntaxcinr 7045 Extend class notation to include right injection of a disjoint union.
 class inr
 
Definitiondf-inl 7046 Left injection of a disjoint union. (Contributed by Mario Carneiro, 21-Jun-2022.)
 |- inl 
 =  ( x  e. 
 _V  |->  <. (/) ,  x >. )
 
Definitiondf-inr 7047 Right injection of a disjoint union. (Contributed by Mario Carneiro, 21-Jun-2022.)
 |- inr 
 =  ( x  e. 
 _V  |->  <. 1o ,  x >. )
 
Theoremdjulclr 7048 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 )
 )
 
Theoremdjurclr 7049 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 )
 )
 
Theoremdjulcl 7050 Left closure of disjoint union. (Contributed by Jim Kingdon, 21-Jun-2022.)
 |-  ( C  e.  A  ->  (inl `  C )  e.  ( A B )
 )
 
Theoremdjurcl 7051 Right closure of disjoint union. (Contributed by Jim Kingdon, 21-Jun-2022.)
 |-  ( C  e.  B  ->  (inr `  C )  e.  ( A B )
 )
 
Theoremdjuf1olem 7052* Lemma for djulf1o 7057 and djurf1o 7058. (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 )
 
Theoremdjuf1olemr 7053* Lemma for djulf1or 7055 and djurf1or 7056. For a version of this lemma with  F defined on  A and no restriction in the conclusion, see djuf1olem 7052. (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 )
 
Theoremdjulclb 7054 Left biconditional closure of disjoint union. (Contributed by Jim Kingdon, 2-Jul-2022.)
 |-  ( C  e.  V  ->  ( C  e.  A  <->  (inl `  C )  e.  ( A B ) ) )
 
Theoremdjulf1or 7055 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 )
 
Theoremdjurf1or 7056 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 )
 
Theoremdjulf1o 7057 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 )
 
Theoremdjurf1o 7058 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 )
 
Theoreminresflem 7059* Lemma for inlresf1 7060 and inrresf1 7061. (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
 
Theoreminlresf1 7060 The left injection restricted to the left class of a disjoint union is an injective function from the left class into the disjoint union. (Contributed by AV, 28-Jun-2022.)
 |-  (inl  |`  A ) : A -1-1-> ( A B )
 
Theoreminrresf1 7061 The right injection restricted to the right class of a disjoint union is an injective function from the right class into the disjoint union. (Contributed by AV, 28-Jun-2022.)
 |-  (inr  |`  B ) : B -1-1-> ( A B )
 
Theoremdjuinr 7062 The ranges of any left and right injections are disjoint. Remark: the extra generality offered by the two restrictions makes the theorem more readily usable (e.g., by djudom 7092 and djufun 7103) while the simpler statement  |-  ( ran inl  i^i 
ran inr )  =  (/) is easily recovered from it by substituting  _V for both  A and  B as done in casefun 7084). (Contributed by BJ and Jim Kingdon, 21-Jun-2022.)
 |-  ( ran  (inl  |`  A )  i^i  ran  (inr  |`  B ) )  =  (/)
 
Theoremdjuin 7063 The images of any classes under right and left injection produce disjoint sets. (Contributed by Jim Kingdon, 21-Jun-2022.) (Proof shortened by BJ, 9-Jul-2023.)
 |-  ( (inl " A )  i^i  (inr " B ) )  =  (/)
 
Theoreminl11 7064 Left injection is one-to-one. (Contributed by Jim Kingdon, 12-Jul-2023.)
 |-  ( ( A  e.  V  /\  B  e.  W )  ->  ( (inl `  A )  =  (inl `  B )  <->  A  =  B ) )
 
Theoremdjuunr 7065 The disjoint union of two classes is the union of the images of those two classes under right and left injection. (Contributed by Jim Kingdon, 22-Jun-2022.) (Proof shortened by BJ, 6-Jul-2022.)
 |-  ( ran  (inl  |`  A )  u.  ran  (inr  |`  B ) )  =  ( A B )
 
Theoremdjuun 7066 The disjoint union of two classes is the union of the images of those two classes under right and left injection. (Contributed by Jim Kingdon, 22-Jun-2022.) (Proof shortened by BJ, 9-Jul-2023.)
 |-  ( (inl " A )  u.  (inr " B ) )  =  ( A B )
 
Theoremeldju 7067* Element of a disjoint union. (Contributed by BJ and Jim Kingdon, 23-Jun-2022.)
 |-  ( C  e.  ( A B )  <->  ( E. x  e.  A  C  =  ( (inl  |`  A ) `  x )  \/  E. x  e.  B  C  =  ( (inr  |`  B ) `  x ) ) )
 
Theoremdjur 7068* A member of a disjoint union can be mapped from one of the classes which produced it. (Contributed by Jim Kingdon, 23-Jun-2022.) Upgrade implication to biconditional and shorten proof. (Revised by BJ, 14-Jul-2023.)
 |-  ( C  e.  ( A B )  <->  ( E. x  e.  A  C  =  (inl `  x )  \/  E. x  e.  B  C  =  (inr `  x )
 ) )
 
2.6.36.3  Universal property of the disjoint union
 
Theoremdjuss 7069 A disjoint union is a subset of a Cartesian product. (Contributed by AV, 25-Jun-2022.)
 |-  ( A B )  C_  ( { (/) ,  1o }  X.  ( A  u.  B ) )
 
Theoremeldju1st 7070 The first component of an element of a disjoint union is either  (/) or  1o. (Contributed by AV, 26-Jun-2022.)
 |-  ( X  e.  ( A B )  ->  (
 ( 1st `  X )  =  (/)  \/  ( 1st `  X )  =  1o ) )
 
Theoremeldju2ndl 7071 The second component of an element of a disjoint union is an element of the left class of the disjoint union if its first component is the empty set. (Contributed by AV, 26-Jun-2022.)
 |-  ( ( X  e.  ( A B )  /\  ( 1st `  X )  =  (/) )  ->  ( 2nd `  X )  e.  A )
 
Theoremeldju2ndr 7072 The second component of an element of a disjoint union is an element of the right class of the disjoint union if its first component is not the empty set. (Contributed by AV, 26-Jun-2022.)
 |-  ( ( X  e.  ( A B )  /\  ( 1st `  X )  =/= 
 (/) )  ->  ( 2nd `  X )  e.  B )
 
Theorem1stinl 7073 The first component of the value of a left injection is the empty set. (Contributed by AV, 27-Jun-2022.)
 |-  ( X  e.  V  ->  ( 1st `  (inl `  X ) )  =  (/) )
 
Theorem2ndinl 7074 The second component of the value of a left injection is its argument. (Contributed by AV, 27-Jun-2022.)
 |-  ( X  e.  V  ->  ( 2nd `  (inl `  X ) )  =  X )
 
Theorem1stinr 7075 The first component of the value of a right injection is  1o. (Contributed by AV, 27-Jun-2022.)
 |-  ( X  e.  V  ->  ( 1st `  (inr `  X ) )  =  1o )
 
Theorem2ndinr 7076 The second component of the value of a right injection is its argument. (Contributed by AV, 27-Jun-2022.)
 |-  ( X  e.  V  ->  ( 2nd `  (inr `  X ) )  =  X )
 
Theoremdjune 7077 Left and right injection never produce equal values. (Contributed by Jim Kingdon, 2-Jul-2022.)
 |-  ( ( A  e.  V  /\  B  e.  W )  ->  (inl `  A )  =/=  (inr `  B ) )
 
Theoremupdjudhf 7078* The mapping of an element of the disjoint union to the value of the corresponding function is a function. (Contributed by AV, 26-Jun-2022.)
 |-  ( ph  ->  F : A --> C )   &    |-  ( ph  ->  G : B --> C )   &    |-  H  =  ( x  e.  ( A B )  |->  if (
 ( 1st `  x )  =  (/) ,  ( F `
  ( 2nd `  x ) ) ,  ( G `  ( 2nd `  x ) ) ) )   =>    |-  ( ph  ->  H :
 ( A B ) --> C )
 
Theoremupdjudhcoinlf 7079* The composition of the mapping of an element of the disjoint union to the value of the corresponding function and the left injection equals the first function. (Contributed by AV, 27-Jun-2022.)
 |-  ( ph  ->  F : A --> C )   &    |-  ( ph  ->  G : B --> C )   &    |-  H  =  ( x  e.  ( A B )  |->  if (
 ( 1st `  x )  =  (/) ,  ( F `
  ( 2nd `  x ) ) ,  ( G `  ( 2nd `  x ) ) ) )   =>    |-  ( ph  ->  ( H  o.  (inl  |`  A ) )  =  F )
 
Theoremupdjudhcoinrg 7080* The composition of the mapping of an element of the disjoint union to the value of the corresponding function and the right injection equals the second function. (Contributed by AV, 27-Jun-2022.)
 |-  ( ph  ->  F : A --> C )   &    |-  ( ph  ->  G : B --> C )   &    |-  H  =  ( x  e.  ( A B )  |->  if (
 ( 1st `  x )  =  (/) ,  ( F `
  ( 2nd `  x ) ) ,  ( G `  ( 2nd `  x ) ) ) )   =>    |-  ( ph  ->  ( H  o.  (inr  |`  B ) )  =  G )
 
Theoremupdjud 7081* Universal property of the disjoint union. (Proposed by BJ, 25-Jun-2022.) (Contributed by AV, 28-Jun-2022.)
 |-  ( ph  ->  F : A --> C )   &    |-  ( ph  ->  G : B --> C )   &    |-  ( ph  ->  A  e.  V )   &    |-  ( ph  ->  B  e.  W )   =>    |-  ( ph  ->  E! h ( h :
 ( A B ) --> C  /\  ( h  o.  (inl  |`  A ) )  =  F  /\  ( h  o.  (inr  |`  B ) )  =  G ) )
 
Syntaxcdjucase 7082 Syntax for the "case" construction.
 class case ( R ,  S )
 
Definitiondf-case 7083 The "case" construction: if  F : A --> X and  G : B --> X are functions, then case ( F ,  G
) : ( A B ) --> X is the natural function obtained by a definition by cases, hence the name. It is the unique function whose existence is asserted by the universal property of disjoint unions updjud 7081. The definition is adapted to make sense also for binary relations (where the universal property also holds). (Contributed by MC and BJ, 10-Jul-2022.)
 |- case
 ( R ,  S )  =  ( ( R  o.  `'inl )  u.  ( S  o.  `'inr ) )
 
Theoremcasefun 7084 The "case" construction of two functions is a function. (Contributed by BJ, 10-Jul-2022.)
 |-  ( ph  ->  Fun  F )   &    |-  ( ph  ->  Fun  G )   =>    |-  ( ph  ->  Fun case ( F ,  G ) )
 
Theoremcasedm 7085 The domain of the "case" construction is the disjoint union of the domains. TODO (although less important):  |-  ran case ( F ,  G )  =  ( ran  F  u.  ran  G ). (Contributed by BJ, 10-Jul-2022.)
 |- 
 dom case ( F ,  G )  =  ( dom  F dom  G )
 
Theoremcaserel 7086 The "case" construction of two relations is a relation, with bounds on its domain and codomain. Typically, the "case" construction is used when both relations have a common codomain. (Contributed by BJ, 10-Jul-2022.)
 |- case
 ( R ,  S )  C_  ( ( dom 
 R dom  S )  X.  ( ran  R  u.  ran  S ) )
 
Theoremcasef 7087 The "case" construction of two functions is a function on the disjoint union of their domains. (Contributed by BJ, 10-Jul-2022.)
 |-  ( ph  ->  F : A --> X )   &    |-  ( ph  ->  G : B --> X )   =>    |-  ( ph  -> case ( F ,  G ) : ( A B ) --> X )
 
Theoremcaseinj 7088 The "case" construction of two injective relations with disjoint ranges is an injective relation. (Contributed by BJ, 10-Jul-2022.)
 |-  ( ph  ->  Fun  `' R )   &    |-  ( ph  ->  Fun  `' S )   &    |-  ( ph  ->  ( ran  R  i^i  ran  S )  =  (/) )   =>    |-  ( ph  ->  Fun  `'case ( R ,  S ) )
 
Theoremcasef1 7089 The "case" construction of two injective functions with disjoint ranges is an injective function. (Contributed by BJ, 10-Jul-2022.)
 |-  ( ph  ->  F : A -1-1-> X )   &    |-  ( ph  ->  G : B -1-1-> X )   &    |-  ( ph  ->  ( ran  F  i^i  ran  G )  =  (/) )   =>    |-  ( ph  -> case ( F ,  G ) : ( A B ) -1-1-> X )
 
Theoremcaseinl 7090 Applying the "case" construction to a left injection. (Contributed by Jim Kingdon, 15-Mar-2023.)
 |-  ( ph  ->  F  Fn  B )   &    |-  ( ph  ->  Fun 
 G )   &    |-  ( ph  ->  A  e.  B )   =>    |-  ( ph  ->  (case ( F ,  G ) `  (inl `  A ) )  =  ( F `  A ) )
 
Theoremcaseinr 7091 Applying the "case" construction to a right injection. (Contributed by Jim Kingdon, 12-Jul-2023.)
 |-  ( ph  ->  Fun  F )   &    |-  ( ph  ->  G  Fn  B )   &    |-  ( ph  ->  A  e.  B )   =>    |-  ( ph  ->  (case ( F ,  G ) `  (inr `  A ) )  =  ( G `  A ) )
 
2.6.36.4  Dominance and equinumerosity properties of disjoint union
 
Theoremdjudom 7092 Dominance law for disjoint union. (Contributed by Jim Kingdon, 25-Jul-2022.)
 |-  ( ( A  ~<_  B  /\  C 
 ~<_  D )  ->  ( A C )  ~<_  ( B D ) )
 
Theoremomp1eomlem 7093* Lemma for omp1eom 7094. (Contributed by Jim Kingdon, 11-Jul-2023.)
 |-  F  =  ( x  e.  om  |->  if ( x  =  (/) ,  (inr `  x ) ,  (inl ` 
 U. x ) ) )   &    |-  S  =  ( x  e.  om  |->  suc 
 x )   &    |-  G  = case ( S ,  (  _I  |` 
 1o ) )   =>    |-  F : om -1-1-onto-> ( om 1o )
 
Theoremomp1eom 7094 Adding one to  om. (Contributed by Jim Kingdon, 10-Jul-2023.)
 |-  ( om 1o )  ~~  om
 
Theoremendjusym 7095 Reversing right and left operands of a disjoint union produces an equinumerous result. (Contributed by Jim Kingdon, 10-Jul-2023.)
 |-  ( ( A  e.  V  /\  B  e.  W )  ->  ( A B ) 
 ~~  ( B A ) )
 
Theoremeninl 7096 Equinumerosity of a set and its image under left injection. (Contributed by Jim Kingdon, 30-Jul-2023.)
 |-  ( A  e.  V  ->  (inl " A )  ~~  A )
 
Theoremeninr 7097 Equinumerosity of a set and its image under right injection. (Contributed by Jim Kingdon, 30-Jul-2023.)
 |-  ( A  e.  V  ->  (inr " A )  ~~  A )
 
Theoremdifinfsnlem 7098* Lemma for difinfsn 7099. The case where we need to swap  B and  (inr `  (/) ) in building the mapping  G. (Contributed by Jim Kingdon, 9-Aug-2023.)
 |-  ( ph  ->  A. x  e.  A  A. y  e.  A DECID  x  =  y )   &    |-  ( ph  ->  B  e.  A )   &    |-  ( ph  ->  F : ( om 1o ) -1-1-> A )   &    |-  ( ph  ->  ( F `  (inr `  (/) ) )  =/=  B )   &    |-  G  =  ( n  e.  om  |->  if (
 ( F `  (inl `  n ) )  =  B ,  ( F `
  (inr `  (/) ) ) ,  ( F `  (inl `  n ) ) ) )   =>    |-  ( ph  ->  G : om -1-1-> ( A  \  { B } ) )
 
Theoremdifinfsn 7099* An infinite set minus one element is infinite. We require that the set has decidable equality. (Contributed by Jim Kingdon, 8-Aug-2023.)
 |-  ( ( A. x  e.  A  A. y  e.  A DECID  x  =  y  /\  om  ~<_  A  /\  B  e.  A )  ->  om  ~<_  ( A 
 \  { B }
 ) )
 
Theoremdifinfinf 7100* An infinite set minus a finite subset is infinite. We require that the set has decidable equality. (Contributed by Jim Kingdon, 8-Aug-2023.)
 |-  ( ( ( A. x  e.  A  A. y  e.  A DECID  x  =  y  /\  om  ~<_  A )  /\  ( B  C_  A  /\  B  e.  Fin ) )  ->  om 
 ~<_  ( A  \  B ) )
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