| Step | Hyp | Ref | Expression | 
						
							| 1 |  | 3optocl.1 |  |-  R = ( D X. F ) | 
						
							| 2 |  | 3optocl.2 |  |-  ( <. x , y >. = A -> ( ph <-> ps ) ) | 
						
							| 3 |  | 3optocl.3 |  |-  ( <. z , w >. = B -> ( ps <-> ch ) ) | 
						
							| 4 |  | 3optocl.4 |  |-  ( <. v , u >. = C -> ( ch <-> th ) ) | 
						
							| 5 |  | 3optocl.5 |  |-  ( ( ( x e. D /\ y e. F ) /\ ( z e. D /\ w e. F ) /\ ( v e. D /\ u e. F ) ) -> ph ) | 
						
							| 6 | 4 | imbi2d |  |-  ( <. v , u >. = C -> ( ( ( A e. R /\ B e. R ) -> ch ) <-> ( ( A e. R /\ B e. R ) -> th ) ) ) | 
						
							| 7 | 2 | imbi2d |  |-  ( <. x , y >. = A -> ( ( ( v e. D /\ u e. F ) -> ph ) <-> ( ( v e. D /\ u e. F ) -> ps ) ) ) | 
						
							| 8 | 3 | imbi2d |  |-  ( <. z , w >. = B -> ( ( ( v e. D /\ u e. F ) -> ps ) <-> ( ( v e. D /\ u e. F ) -> ch ) ) ) | 
						
							| 9 | 5 | 3expia |  |-  ( ( ( x e. D /\ y e. F ) /\ ( z e. D /\ w e. F ) ) -> ( ( v e. D /\ u e. F ) -> ph ) ) | 
						
							| 10 | 1 7 8 9 | 2optocl |  |-  ( ( A e. R /\ B e. R ) -> ( ( v e. D /\ u e. F ) -> ch ) ) | 
						
							| 11 | 10 | com12 |  |-  ( ( v e. D /\ u e. F ) -> ( ( A e. R /\ B e. R ) -> ch ) ) | 
						
							| 12 | 1 6 11 | optocl |  |-  ( C e. R -> ( ( A e. R /\ B e. R ) -> th ) ) | 
						
							| 13 | 12 | impcom |  |-  ( ( ( A e. R /\ B e. R ) /\ C e. R ) -> th ) | 
						
							| 14 | 13 | 3impa |  |-  ( ( A e. R /\ B e. R /\ C e. R ) -> th ) |