| Step | Hyp | Ref | Expression | 
						
							| 1 |  | kbfval |  |-  ( ( A e. ~H /\ B e. ~H ) -> ( A ketbra B ) = ( x e. ~H |-> ( ( x .ih B ) .h A ) ) ) | 
						
							| 2 | 1 | fveq1d |  |-  ( ( A e. ~H /\ B e. ~H ) -> ( ( A ketbra B ) ` C ) = ( ( x e. ~H |-> ( ( x .ih B ) .h A ) ) ` C ) ) | 
						
							| 3 |  | oveq1 |  |-  ( x = C -> ( x .ih B ) = ( C .ih B ) ) | 
						
							| 4 | 3 | oveq1d |  |-  ( x = C -> ( ( x .ih B ) .h A ) = ( ( C .ih B ) .h A ) ) | 
						
							| 5 |  | eqid |  |-  ( x e. ~H |-> ( ( x .ih B ) .h A ) ) = ( x e. ~H |-> ( ( x .ih B ) .h A ) ) | 
						
							| 6 |  | ovex |  |-  ( ( C .ih B ) .h A ) e. _V | 
						
							| 7 | 4 5 6 | fvmpt |  |-  ( C e. ~H -> ( ( x e. ~H |-> ( ( x .ih B ) .h A ) ) ` C ) = ( ( C .ih B ) .h A ) ) | 
						
							| 8 | 2 7 | sylan9eq |  |-  ( ( ( A e. ~H /\ B e. ~H ) /\ C e. ~H ) -> ( ( A ketbra B ) ` C ) = ( ( C .ih B ) .h A ) ) | 
						
							| 9 | 8 | 3impa |  |-  ( ( A e. ~H /\ B e. ~H /\ C e. ~H ) -> ( ( A ketbra B ) ` C ) = ( ( C .ih B ) .h A ) ) |