| Step | Hyp | Ref | Expression | 
						
							| 1 |  | vex |  |-  x e. _V | 
						
							| 2 |  | vex |  |-  y e. _V | 
						
							| 3 | 1 2 | pm3.2i |  |-  ( x e. _V /\ y e. _V ) | 
						
							| 4 | 3 | a1i |  |-  ( ph -> ( x e. _V /\ y e. _V ) ) | 
						
							| 5 | 4 | ssopab2i |  |-  { <. x , y >. | ph } C_ { <. x , y >. | ( x e. _V /\ y e. _V ) } | 
						
							| 6 | 3 | biantru |  |-  ( z = <. x , y >. <-> ( z = <. x , y >. /\ ( x e. _V /\ y e. _V ) ) ) | 
						
							| 7 | 6 | exbii |  |-  ( E. y z = <. x , y >. <-> E. y ( z = <. x , y >. /\ ( x e. _V /\ y e. _V ) ) ) | 
						
							| 8 | 7 | exbii |  |-  ( E. x E. y z = <. x , y >. <-> E. x E. y ( z = <. x , y >. /\ ( x e. _V /\ y e. _V ) ) ) | 
						
							| 9 | 8 | abbii |  |-  { z | E. x E. y z = <. x , y >. } = { z | E. x E. y ( z = <. x , y >. /\ ( x e. _V /\ y e. _V ) ) } | 
						
							| 10 |  | ax6ev |  |-  E. u u = x | 
						
							| 11 |  | equcom |  |-  ( u = x <-> x = u ) | 
						
							| 12 | 11 | exbii |  |-  ( E. u u = x <-> E. u x = u ) | 
						
							| 13 | 10 12 | mpbi |  |-  E. u x = u | 
						
							| 14 |  | ax6ev |  |-  E. v v = y | 
						
							| 15 |  | equcom |  |-  ( v = y <-> y = v ) | 
						
							| 16 | 15 | exbii |  |-  ( E. v v = y <-> E. v y = v ) | 
						
							| 17 | 14 16 | mpbi |  |-  E. v y = v | 
						
							| 18 |  | idn1 |  |-  (. y = v ->. y = v ). | 
						
							| 19 |  | opeq2 |  |-  ( y = v -> <. x , y >. = <. x , v >. ) | 
						
							| 20 | 18 19 | e1a |  |-  (. y = v ->. <. x , y >. = <. x , v >. ). | 
						
							| 21 |  | idn2 |  |-  (. y = v ,. x = u ->. x = u ). | 
						
							| 22 |  | opeq1 |  |-  ( x = u -> <. x , v >. = <. u , v >. ) | 
						
							| 23 | 21 22 | e2 |  |-  (. y = v ,. x = u ->. <. x , v >. = <. u , v >. ). | 
						
							| 24 |  | eqeq1 |  |-  ( <. x , y >. = <. x , v >. -> ( <. x , y >. = <. u , v >. <-> <. x , v >. = <. u , v >. ) ) | 
						
							| 25 | 24 | biimprd |  |-  ( <. x , y >. = <. x , v >. -> ( <. x , v >. = <. u , v >. -> <. x , y >. = <. u , v >. ) ) | 
						
							| 26 | 20 23 25 | e12 |  |-  (. y = v ,. x = u ->. <. x , y >. = <. u , v >. ). | 
						
							| 27 |  | eqeq2 |  |-  ( <. x , y >. = <. u , v >. -> ( z = <. x , y >. <-> z = <. u , v >. ) ) | 
						
							| 28 | 27 | biimpd |  |-  ( <. x , y >. = <. u , v >. -> ( z = <. x , y >. -> z = <. u , v >. ) ) | 
						
							| 29 | 26 28 | e2 |  |-  (. y = v ,. x = u ->. ( z = <. x , y >. -> z = <. u , v >. ) ). | 
						
							| 30 | 29 | in2 |  |-  (. y = v ->. ( x = u -> ( z = <. x , y >. -> z = <. u , v >. ) ) ). | 
						
							| 31 | 30 | in1 |  |-  ( y = v -> ( x = u -> ( z = <. x , y >. -> z = <. u , v >. ) ) ) | 
						
							| 32 | 31 | eximi |  |-  ( E. v y = v -> E. v ( x = u -> ( z = <. x , y >. -> z = <. u , v >. ) ) ) | 
						
							| 33 | 17 32 | ax-mp |  |-  E. v ( x = u -> ( z = <. x , y >. -> z = <. u , v >. ) ) | 
						
							| 34 | 33 | 19.37iv |  |-  ( x = u -> E. v ( z = <. x , y >. -> z = <. u , v >. ) ) | 
						
							| 35 |  | 19.37v |  |-  ( E. v ( z = <. x , y >. -> z = <. u , v >. ) <-> ( z = <. x , y >. -> E. v z = <. u , v >. ) ) | 
						
							| 36 | 35 | biimpi |  |-  ( E. v ( z = <. x , y >. -> z = <. u , v >. ) -> ( z = <. x , y >. -> E. v z = <. u , v >. ) ) | 
						
							| 37 | 34 36 | syl |  |-  ( x = u -> ( z = <. x , y >. -> E. v z = <. u , v >. ) ) | 
						
							| 38 | 37 | eximi |  |-  ( E. u x = u -> E. u ( z = <. x , y >. -> E. v z = <. u , v >. ) ) | 
						
							| 39 | 13 38 | ax-mp |  |-  E. u ( z = <. x , y >. -> E. v z = <. u , v >. ) | 
						
							| 40 | 39 | 19.37iv |  |-  ( z = <. x , y >. -> E. u E. v z = <. u , v >. ) | 
						
							| 41 | 40 | eximi |  |-  ( E. y z = <. x , y >. -> E. y E. u E. v z = <. u , v >. ) | 
						
							| 42 |  | 19.9v |  |-  ( E. y E. u E. v z = <. u , v >. <-> E. u E. v z = <. u , v >. ) | 
						
							| 43 | 42 | biimpi |  |-  ( E. y E. u E. v z = <. u , v >. -> E. u E. v z = <. u , v >. ) | 
						
							| 44 | 41 43 | syl |  |-  ( E. y z = <. x , y >. -> E. u E. v z = <. u , v >. ) | 
						
							| 45 | 44 | eximi |  |-  ( E. x E. y z = <. x , y >. -> E. x E. u E. v z = <. u , v >. ) | 
						
							| 46 |  | 19.9v |  |-  ( E. x E. u E. v z = <. u , v >. <-> E. u E. v z = <. u , v >. ) | 
						
							| 47 | 46 | biimpi |  |-  ( E. x E. u E. v z = <. u , v >. -> E. u E. v z = <. u , v >. ) | 
						
							| 48 | 45 47 | syl |  |-  ( E. x E. y z = <. x , y >. -> E. u E. v z = <. u , v >. ) | 
						
							| 49 | 48 | ss2abi |  |-  { z | E. x E. y z = <. x , y >. } C_ { z | E. u E. v z = <. u , v >. } | 
						
							| 50 | 9 49 | eqsstrri |  |-  { z | E. x E. y ( z = <. x , y >. /\ ( x e. _V /\ y e. _V ) ) } C_ { z | E. u E. v z = <. u , v >. } | 
						
							| 51 |  | vex |  |-  u e. _V | 
						
							| 52 |  | vex |  |-  v e. _V | 
						
							| 53 | 51 52 | pm3.2i |  |-  ( u e. _V /\ v e. _V ) | 
						
							| 54 | 53 | biantru |  |-  ( z = <. u , v >. <-> ( z = <. u , v >. /\ ( u e. _V /\ v e. _V ) ) ) | 
						
							| 55 | 54 | exbii |  |-  ( E. v z = <. u , v >. <-> E. v ( z = <. u , v >. /\ ( u e. _V /\ v e. _V ) ) ) | 
						
							| 56 | 55 | exbii |  |-  ( E. u E. v z = <. u , v >. <-> E. u E. v ( z = <. u , v >. /\ ( u e. _V /\ v e. _V ) ) ) | 
						
							| 57 | 56 | abbii |  |-  { z | E. u E. v z = <. u , v >. } = { z | E. u E. v ( z = <. u , v >. /\ ( u e. _V /\ v e. _V ) ) } | 
						
							| 58 | 50 57 | sseqtri |  |-  { z | E. x E. y ( z = <. x , y >. /\ ( x e. _V /\ y e. _V ) ) } C_ { z | E. u E. v ( z = <. u , v >. /\ ( u e. _V /\ v e. _V ) ) } | 
						
							| 59 |  | df-opab |  |-  { <. x , y >. | ( x e. _V /\ y e. _V ) } = { z | E. x E. y ( z = <. x , y >. /\ ( x e. _V /\ y e. _V ) ) } | 
						
							| 60 |  | df-opab |  |-  { <. u , v >. | ( u e. _V /\ v e. _V ) } = { z | E. u E. v ( z = <. u , v >. /\ ( u e. _V /\ v e. _V ) ) } | 
						
							| 61 | 58 59 60 | 3sstr4i |  |-  { <. x , y >. | ( x e. _V /\ y e. _V ) } C_ { <. u , v >. | ( u e. _V /\ v e. _V ) } | 
						
							| 62 |  | df-xp |  |-  ( _V X. _V ) = { <. u , v >. | ( u e. _V /\ v e. _V ) } | 
						
							| 63 | 62 | eqcomi |  |-  { <. u , v >. | ( u e. _V /\ v e. _V ) } = ( _V X. _V ) | 
						
							| 64 | 61 63 | sseqtri |  |-  { <. x , y >. | ( x e. _V /\ y e. _V ) } C_ ( _V X. _V ) | 
						
							| 65 | 5 64 | sstri |  |-  { <. x , y >. | ph } C_ ( _V X. _V ) | 
						
							| 66 |  | df-rel |  |-  ( Rel { <. x , y >. | ph } <-> { <. x , y >. | ph } C_ ( _V X. _V ) ) | 
						
							| 67 | 66 | biimpri |  |-  ( { <. x , y >. | ph } C_ ( _V X. _V ) -> Rel { <. x , y >. | ph } ) | 
						
							| 68 | 65 67 | e0a |  |-  Rel { <. x , y >. | ph } |