| 1:: | |- (. y = v ->. y = v ). | 
 | 2:1: | |- (. y = v ->. <. x ,. y >. = <. x ,. v
       >. ). | 
 | 3:: | |- (. y = v ,. x = u ->. x = u ). | 
 | 4:3: | |- (. y = v ,. x = u ->. <. x ,. v >. = <.
      
       u , v >. ). | 
 | 5:2,4: | |- (. y = v ,. x = u ->. <. x ,. y >. = <.
      
       u , v >. ). | 
 | 6:5: | |- (. y = v ,. x = u ->. ( z = <. x ,. y
       >. -> z = <. u , v >. ) ). | 
 | 7:6: | |- (. y = v ->. ( x = u -> ( z = <. x ,.
       y >. -> z = <. u , v >. ) ) ). | 
 | 8:7: | |- ( y = v -> ( x = u -> ( z = <. x ,. y
       >. -> z = <. u , v >. ) ) ) | 
 | 9:8: | |- ( E. v y = v ->  E. v ( x = u -> ( z
       = <. x , y >. -> z = <. u , v >. ) ) ) | 
 | 90:: | |- ( v = y <-> y = v ) | 
 | 91:90: | |- ( E. v v = y <-> E. v y = v ) | 
 | 92:: | |- E. v v = y | 
 | 10:91,92: | |- E. v y = v | 
 | 11:9,10: | |- E. v ( x = u -> ( z = <. x ,. y >. ->
       z = <. u , v >. ) ) | 
 | 12:11: | |- ( x = u -> E. v ( z = <. x ,. y >. ->
       z = <. u , v >. ) ) | 
 | 13:: | |- ( E. v ( z = <. x ,. y >. -> z = <. u
       , v >. ) -> ( z = <. x , y >. -> E. v z = <. u , v >. ) ) | 
 | 14:12,13: | |- ( x = u -> ( z = <. x ,. y >. -> E. v
       z = <. u , v >. ) ) | 
 | 15:14: | |- ( E. u x = u -> E. u ( z = <. x ,. y
       >. -> E. v z = <. u , v >. ) ) | 
 | 150:: | |- ( u = x <-> x = u ) | 
 | 151:150: | |- ( E. u u = x <-> E. u x = u ) | 
 | 152:: | |- E. u u = x | 
 | 16:151,152: | |- E. u x = u | 
 | 17:15,16: | |- E. u ( z = <. x ,. y >. -> E. v z = <.
      
       u , v >. ) | 
 | 18:17: | |- ( z = <. x ,. y >. -> E. u E. v z = <.
      
       u , v >. ) | 
 | 19:18: | |- ( E. y z = <. x ,. y >. -> E. y E. u
       E. v z = <. u , v >. ) | 
 | 20:: | |- ( E. y E. u E. v z = <. u ,. v >. ->
       E. u E. v z = <. u , v >. ) | 
 | 21:19,20: | |- ( E. y z = <. x ,. y >. -> E. u E. v z
      
       = <. u , v >. ) | 
 | 22:21: | |- ( E. x E. y z = <. x ,. y >. -> E. x
       E. u E. v z = <. u , v >. ) | 
 | 23:: | |- ( E. x E. u E. v z = <. u ,. v >. ->
       E. u E. v z = <. u , v >. ) | 
 | 24:22,23: | |- ( E. x E. y z = <. x ,. y >. -> E. u
       E. v z = <. u , v >. ) | 
 | 25:24: | |- { z | E. x E. y z = <. x ,. y >. } C_
       { z | E. u E. v z = <. u , v >. } | 
 | 26:: | |- x e.V | 
 | 27:: | |- y e. V | 
 | 28:26,27: | |- ( x e.V /\ y e. V ) | 
 | 29:28: | |- ( z = <. x ,. y >. <-> ( z = <. x ,. y
      
       >. /\ ( x e.V /\ y e. V ) ) ) | 
 | 30:29: | |- ( E. y z = <. x ,. y >. <-> E. y ( z =
      
       <. x , y >. /\ ( x e.V /\ y e. V ) ) ) | 
 | 31:30: | |- ( E. x E. y z = <. x ,. y >. <-> E. x
       E. y ( z = <. x , y >. /\ ( x e.V /\ y e. V ) ) ) | 
 | 32:31: | |- { z | E. x E. y z = <. x ,. y >. } = {
      
       z | E. x E. y ( z = <. x , y >. /\ ( x e.V /\ y e. V ) ) } | 
 | 320:25,32: | |- { z | E. x E. y ( z = <. x ,. y >. /\
       ( x e.V /\ y e. V ) ) } C_ { z | E. u E. v z = <. u , v >. } | 
 | 33:: | |- u e.V | 
 | 34:: | |- v e. V | 
 | 35:33,34: | |- ( u e.V /\ v e. V ) | 
 | 36:35: | |- ( z = <. u ,. v >. <-> ( z = <. u ,. v
      
       >. /\ ( u e.V /\ v e. V ) ) ) | 
 | 37:36: | |- ( E. v z = <. u ,. v >. <-> E. v ( z =
      
       <. u , v >. /\ ( u e.V /\ v e. V ) ) ) | 
 | 38:37: | |- ( E. u E. v z = <. u ,. v >. <-> E. u
       E. v ( z = <. u , v >. /\ ( u e.V /\ v e. V ) ) ) | 
 | 39:38: | |- { z | E. u E. v z = <. u ,. v >. } = {
      
       z | E. u E. v ( z = <. u , v >. /\ ( u e.V /\ v e. V ) ) } | 
 | 40:320,39: | |- { 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 ) ) } | 
 | 41:: | |- { <. x ,. y >. | ( x e.V /\ y e. V
       ) } = { z | E. x E. y ( z = <. x , y >. /\ ( x e.V /\ y e. V ) )
       } | 
 | 42:: | |- { <. u ,. v >. | ( u e.V /\ v e. V
       ) } = { z | E. u E. v ( z = <. u , v >. /\ ( u e.V /\ v e. V ) )
       } | 
 | 43:40,41,42: | |- { <. x ,. y >. | ( x e.V /\ y e. V
       ) } C_ { <. u , v >. | ( u e.V /\ v e. V ) } | 
 | 44:: | |- { <. u ,. v >. | ( u e.V /\ v e. V
       ) } = (V X. V ) | 
 | 45:43,44: | |- { <. x ,. y >. | ( x e.V /\ y e. V
       ) } C_ (V X. V ) | 
 | 46:28: | |- ( ph -> ( x e.V /\ y e. V ) ) | 
 | 47:46: | |- { <. x ,. y >. | ph } C_ { <. x ,. y >.
      
       | ( x e.V /\ y e. V ) } | 
 | 48:45,47: | |- { <. x ,. y >. | ph } C_ (V X. V ) | 
 | qed:48: | |- Rel { <. x ,. y >. | ph } |