| Step | Hyp | Ref | Expression | 
						
							| 1 |  | bicom |  |-  ( ( th <-> ta ) <-> ( ta <-> th ) ) | 
						
							| 2 |  | imbi2 |  |-  ( ( ( th <-> ta ) <-> ( ta <-> th ) ) -> ( ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) <-> ( ( ph /\ ps /\ ch ) -> ( ta <-> th ) ) ) ) | 
						
							| 3 | 2 | biimpcd |  |-  ( ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) -> ( ( ( th <-> ta ) <-> ( ta <-> th ) ) -> ( ( ph /\ ps /\ ch ) -> ( ta <-> th ) ) ) ) | 
						
							| 4 | 1 3 | mpi |  |-  ( ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) -> ( ( ph /\ ps /\ ch ) -> ( ta <-> th ) ) ) | 
						
							| 5 | 4 | 3expd |  |-  ( ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) -> ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) ) | 
						
							| 6 |  | 3impexp |  |-  ( ( ( ph /\ ps /\ ch ) -> ( ta <-> th ) ) <-> ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) ) | 
						
							| 7 | 6 | biimpri |  |-  ( ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) -> ( ( ph /\ ps /\ ch ) -> ( ta <-> th ) ) ) | 
						
							| 8 | 7 1 | imbitrrdi |  |-  ( ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) -> ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) ) | 
						
							| 9 | 5 8 | impbii |  |-  ( ( ( ph /\ ps /\ ch ) -> ( th <-> ta ) ) <-> ( ph -> ( ps -> ( ch -> ( ta <-> th ) ) ) ) ) |