| Step | Hyp | Ref | Expression | 
						
							| 1 |  | idn1 |  |-  (. ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) ->. ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) ). | 
						
							| 2 |  | bicom |  |-  ( ( th <-> ta ) <-> ( ta <-> th ) ) | 
						
							| 3 |  | imbi2 |  |-  ( ( ( th <-> ta ) <-> ( ta <-> th ) ) -> ( ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) <-> ( ( ph /\ ps /\ ch ) -> ( ta <-> th ) ) ) ) | 
						
							| 4 | 3 | biimpcd |  |-  ( ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) -> ( ( ( th <-> ta ) <-> ( ta <-> th ) ) -> ( ( ph /\ ps /\ ch ) -> ( ta <-> th ) ) ) ) | 
						
							| 5 | 1 2 4 | e10 |  |-  (. ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) ->. ( ( ph /\ ps /\ ch ) -> ( ta <-> th ) ) ). | 
						
							| 6 |  | 3impexp |  |-  ( ( ( ph /\ ps /\ ch ) -> ( ta <-> th ) ) <-> ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) ) | 
						
							| 7 | 6 | biimpi |  |-  ( ( ( ph /\ ps /\ ch ) -> ( ta <-> th ) ) -> ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) ) | 
						
							| 8 | 5 7 | e1a |  |-  (. ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) ->. ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) ). | 
						
							| 9 | 8 | in1 |  |-  ( ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) -> ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) ) | 
						
							| 10 |  | idn1 |  |-  (. ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) ->. ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) ). | 
						
							| 11 | 6 | biimpri |  |-  ( ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) -> ( ( ph /\ ps /\ ch ) -> ( ta <-> th ) ) ) | 
						
							| 12 | 10 11 | e1a |  |-  (. ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) ->. ( ( ph /\ ps /\ ch ) -> ( ta <-> th ) ) ). | 
						
							| 13 | 3 | biimprcd |  |-  ( ( ( ph /\ ps /\ ch ) -> ( ta <-> th ) ) -> ( ( ( th <-> ta ) <-> ( ta <-> th ) ) -> ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) ) ) | 
						
							| 14 | 12 2 13 | e10 |  |-  (. ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) ->. ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) ). | 
						
							| 15 | 14 | in1 |  |-  ( ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) -> ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) ) | 
						
							| 16 |  | impbi |  |-  ( ( ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) -> ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) ) -> ( ( ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) -> ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) ) -> ( ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) <-> ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) ) ) ) | 
						
							| 17 | 9 15 16 | e00 |  |-  ( ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) <-> ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) ) |