| Step | Hyp | Ref | Expression | 
						
							| 1 |  | idn1 |  |-  (. A e. B ->. A e. B ). | 
						
							| 2 |  | idn2 |  |-  (. A e. B ,. [. A / x ]. ( ph -> ( ps -> ch ) ) ->. [. A / x ]. ( ph -> ( ps -> ch ) ) ). | 
						
							| 3 |  | sbcimg |  |-  ( A e. B -> ( [. A / x ]. ( ph -> ( ps -> ch ) ) <-> ( [. A / x ]. ph -> [. A / x ]. ( ps -> ch ) ) ) ) | 
						
							| 4 | 3 | biimpd |  |-  ( A e. B -> ( [. A / x ]. ( ph -> ( ps -> ch ) ) -> ( [. A / x ]. ph -> [. A / x ]. ( ps -> ch ) ) ) ) | 
						
							| 5 | 1 2 4 | e12 |  |-  (. A e. B ,. [. A / x ]. ( ph -> ( ps -> ch ) ) ->. ( [. A / x ]. ph -> [. A / x ]. ( ps -> ch ) ) ). | 
						
							| 6 |  | sbcimg |  |-  ( A e. B -> ( [. A / x ]. ( ps -> ch ) <-> ( [. A / x ]. ps -> [. A / x ]. ch ) ) ) | 
						
							| 7 | 1 6 | e1a |  |-  (. A e. B ->. ( [. A / x ]. ( ps -> ch ) <-> ( [. A / x ]. ps -> [. A / x ]. ch ) ) ). | 
						
							| 8 |  | imbi2 |  |-  ( ( [. A / x ]. ( ps -> ch ) <-> ( [. A / x ]. ps -> [. A / x ]. ch ) ) -> ( ( [. A / x ]. ph -> [. A / x ]. ( ps -> ch ) ) <-> ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) ) ) | 
						
							| 9 | 8 | biimpcd |  |-  ( ( [. A / x ]. ph -> [. A / x ]. ( ps -> ch ) ) -> ( ( [. A / x ]. ( ps -> ch ) <-> ( [. A / x ]. ps -> [. A / x ]. ch ) ) -> ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) ) ) | 
						
							| 10 | 5 7 9 | e21 |  |-  (. A e. B ,. [. A / x ]. ( ph -> ( ps -> ch ) ) ->. ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) ). | 
						
							| 11 | 10 | in2 |  |-  (. A e. B ->. ( [. A / x ]. ( ph -> ( ps -> ch ) ) -> ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) ) ). | 
						
							| 12 |  | idn2 |  |-  (. A e. B ,. ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) ->. ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) ). | 
						
							| 13 |  | biimpr |  |-  ( ( [. A / x ]. ( ps -> ch ) <-> ( [. A / x ]. ps -> [. A / x ]. ch ) ) -> ( ( [. A / x ]. ps -> [. A / x ]. ch ) -> [. A / x ]. ( ps -> ch ) ) ) | 
						
							| 14 | 13 | imim2d |  |-  ( ( [. A / x ]. ( ps -> ch ) <-> ( [. A / x ]. ps -> [. A / x ]. ch ) ) -> ( ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) -> ( [. A / x ]. ph -> [. A / x ]. ( ps -> ch ) ) ) ) | 
						
							| 15 | 7 12 14 | e12 |  |-  (. A e. B ,. ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) ->. ( [. A / x ]. ph -> [. A / x ]. ( ps -> ch ) ) ). | 
						
							| 16 | 1 3 | e1a |  |-  (. A e. B ->. ( [. A / x ]. ( ph -> ( ps -> ch ) ) <-> ( [. A / x ]. ph -> [. A / x ]. ( ps -> ch ) ) ) ). | 
						
							| 17 |  | biimpr |  |-  ( ( [. A / x ]. ( ph -> ( ps -> ch ) ) <-> ( [. A / x ]. ph -> [. A / x ]. ( ps -> ch ) ) ) -> ( ( [. A / x ]. ph -> [. A / x ]. ( ps -> ch ) ) -> [. A / x ]. ( ph -> ( ps -> ch ) ) ) ) | 
						
							| 18 | 17 | com12 |  |-  ( ( [. A / x ]. ph -> [. A / x ]. ( ps -> ch ) ) -> ( ( [. A / x ]. ( ph -> ( ps -> ch ) ) <-> ( [. A / x ]. ph -> [. A / x ]. ( ps -> ch ) ) ) -> [. A / x ]. ( ph -> ( ps -> ch ) ) ) ) | 
						
							| 19 | 15 16 18 | e21 |  |-  (. A e. B ,. ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) ->. [. A / x ]. ( ph -> ( ps -> ch ) ) ). | 
						
							| 20 | 19 | in2 |  |-  (. A e. B ->. ( ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) -> [. A / x ]. ( ph -> ( ps -> ch ) ) ) ). | 
						
							| 21 |  | impbi |  |-  ( ( [. A / x ]. ( ph -> ( ps -> ch ) ) -> ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) ) -> ( ( ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) -> [. A / x ]. ( ph -> ( ps -> ch ) ) ) -> ( [. A / x ]. ( ph -> ( ps -> ch ) ) <-> ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) ) ) ) | 
						
							| 22 | 11 20 21 | e11 |  |-  (. A e. B ->. ( [. A / x ]. ( ph -> ( ps -> ch ) ) <-> ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) ) ). | 
						
							| 23 | 22 | in1 |  |-  ( A e. B -> ( [. A / x ]. ( ph -> ( ps -> ch ) ) <-> ( [. A / x ]. ph -> ( [. A / x ]. ps -> [. A / x ]. ch ) ) ) ) |