| Step | Hyp | Ref | Expression | 
						
							| 1 |  | vex |  |-  x e. _V | 
						
							| 2 |  | vex |  |-  y e. _V | 
						
							| 3 | 1 2 | opnzi |  |-  <. x , y >. =/= (/) | 
						
							| 4 |  | simpl |  |-  ( ( (/) = <. x , y >. /\ ph ) -> (/) = <. x , y >. ) | 
						
							| 5 | 4 | eqcomd |  |-  ( ( (/) = <. x , y >. /\ ph ) -> <. x , y >. = (/) ) | 
						
							| 6 | 5 | necon3ai |  |-  ( <. x , y >. =/= (/) -> -. ( (/) = <. x , y >. /\ ph ) ) | 
						
							| 7 | 3 6 | ax-mp |  |-  -. ( (/) = <. x , y >. /\ ph ) | 
						
							| 8 | 7 | nex |  |-  -. E. y ( (/) = <. x , y >. /\ ph ) | 
						
							| 9 | 8 | nex |  |-  -. E. x E. y ( (/) = <. x , y >. /\ ph ) | 
						
							| 10 |  | elopab |  |-  ( (/) e. { <. x , y >. | ph } <-> E. x E. y ( (/) = <. x , y >. /\ ph ) ) | 
						
							| 11 | 9 10 | mtbir |  |-  -. (/) e. { <. x , y >. | ph } | 
						
							| 12 |  | eleq1 |  |-  ( <. A , B >. = (/) -> ( <. A , B >. e. { <. x , y >. | ph } <-> (/) e. { <. x , y >. | ph } ) ) | 
						
							| 13 | 11 12 | mtbiri |  |-  ( <. A , B >. = (/) -> -. <. A , B >. e. { <. x , y >. | ph } ) | 
						
							| 14 | 13 | necon2ai |  |-  ( <. A , B >. e. { <. x , y >. | ph } -> <. A , B >. =/= (/) ) | 
						
							| 15 |  | opnz |  |-  ( <. A , B >. =/= (/) <-> ( A e. _V /\ B e. _V ) ) | 
						
							| 16 | 14 15 | sylib |  |-  ( <. A , B >. e. { <. x , y >. | ph } -> ( A e. _V /\ B e. _V ) ) | 
						
							| 17 |  | sbcex |  |-  ( [. A / x ]. [. B / y ]. ph -> A e. _V ) | 
						
							| 18 |  | spesbc |  |-  ( [. A / x ]. [. B / y ]. ph -> E. x [. B / y ]. ph ) | 
						
							| 19 |  | sbcex |  |-  ( [. B / y ]. ph -> B e. _V ) | 
						
							| 20 | 19 | exlimiv |  |-  ( E. x [. B / y ]. ph -> B e. _V ) | 
						
							| 21 | 18 20 | syl |  |-  ( [. A / x ]. [. B / y ]. ph -> B e. _V ) | 
						
							| 22 | 17 21 | jca |  |-  ( [. A / x ]. [. B / y ]. ph -> ( A e. _V /\ B e. _V ) ) | 
						
							| 23 |  | opeq1 |  |-  ( z = A -> <. z , w >. = <. A , w >. ) | 
						
							| 24 | 23 | eleq1d |  |-  ( z = A -> ( <. z , w >. e. { <. x , y >. | ph } <-> <. A , w >. e. { <. x , y >. | ph } ) ) | 
						
							| 25 |  | dfsbcq2 |  |-  ( z = A -> ( [ z / x ] [ w / y ] ph <-> [. A / x ]. [ w / y ] ph ) ) | 
						
							| 26 | 24 25 | bibi12d |  |-  ( z = A -> ( ( <. z , w >. e. { <. x , y >. | ph } <-> [ z / x ] [ w / y ] ph ) <-> ( <. A , w >. e. { <. x , y >. | ph } <-> [. A / x ]. [ w / y ] ph ) ) ) | 
						
							| 27 |  | opeq2 |  |-  ( w = B -> <. A , w >. = <. A , B >. ) | 
						
							| 28 | 27 | eleq1d |  |-  ( w = B -> ( <. A , w >. e. { <. x , y >. | ph } <-> <. A , B >. e. { <. x , y >. | ph } ) ) | 
						
							| 29 |  | dfsbcq2 |  |-  ( w = B -> ( [ w / y ] ph <-> [. B / y ]. ph ) ) | 
						
							| 30 | 29 | sbcbidv |  |-  ( w = B -> ( [. A / x ]. [ w / y ] ph <-> [. A / x ]. [. B / y ]. ph ) ) | 
						
							| 31 | 28 30 | bibi12d |  |-  ( w = B -> ( ( <. A , w >. e. { <. x , y >. | ph } <-> [. A / x ]. [ w / y ] ph ) <-> ( <. A , B >. e. { <. x , y >. | ph } <-> [. A / x ]. [. B / y ]. ph ) ) ) | 
						
							| 32 |  | vopelopabsb |  |-  ( <. z , w >. e. { <. x , y >. | ph } <-> [ z / x ] [ w / y ] ph ) | 
						
							| 33 | 26 31 32 | vtocl2g |  |-  ( ( A e. _V /\ B e. _V ) -> ( <. A , B >. e. { <. x , y >. | ph } <-> [. A / x ]. [. B / y ]. ph ) ) | 
						
							| 34 | 16 22 33 | pm5.21nii |  |-  ( <. A , B >. e. { <. x , y >. | ph } <-> [. A / x ]. [. B / y ]. ph ) |