| Step | Hyp | Ref | Expression | 
						
							| 0 |  | ccup |  |-  Cup | 
						
							| 1 |  | cvv |  |-  _V | 
						
							| 2 | 1 1 | cxp |  |-  ( _V X. _V ) | 
						
							| 3 | 2 1 | cxp |  |-  ( ( _V X. _V ) X. _V ) | 
						
							| 4 |  | cep |  |-  _E | 
						
							| 5 | 1 4 | ctxp |  |-  ( _V (x) _E ) | 
						
							| 6 |  | c1st |  |-  1st | 
						
							| 7 | 6 | ccnv |  |-  `' 1st | 
						
							| 8 | 7 4 | ccom |  |-  ( `' 1st o. _E ) | 
						
							| 9 |  | c2nd |  |-  2nd | 
						
							| 10 | 9 | ccnv |  |-  `' 2nd | 
						
							| 11 | 10 4 | ccom |  |-  ( `' 2nd o. _E ) | 
						
							| 12 | 8 11 | cun |  |-  ( ( `' 1st o. _E ) u. ( `' 2nd o. _E ) ) | 
						
							| 13 | 12 1 | ctxp |  |-  ( ( ( `' 1st o. _E ) u. ( `' 2nd o. _E ) ) (x) _V ) | 
						
							| 14 | 5 13 | csymdif |  |-  ( ( _V (x) _E ) /_\ ( ( ( `' 1st o. _E ) u. ( `' 2nd o. _E ) ) (x) _V ) ) | 
						
							| 15 | 14 | crn |  |-  ran ( ( _V (x) _E ) /_\ ( ( ( `' 1st o. _E ) u. ( `' 2nd o. _E ) ) (x) _V ) ) | 
						
							| 16 | 3 15 | cdif |  |-  ( ( ( _V X. _V ) X. _V ) \ ran ( ( _V (x) _E ) /_\ ( ( ( `' 1st o. _E ) u. ( `' 2nd o. _E ) ) (x) _V ) ) ) | 
						
							| 17 | 0 16 | wceq |  |-  Cup = ( ( ( _V X. _V ) X. _V ) \ ran ( ( _V (x) _E ) /_\ ( ( ( `' 1st o. _E ) u. ( `' 2nd o. _E ) ) (x) _V ) ) ) |