Step |
Hyp |
Ref |
Expression |
1 |
|
an31 |
|- ( ( ( ph /\ ps ) /\ ch ) <-> ( ( ch /\ ps ) /\ ph ) ) |
2 |
|
notbi |
|- ( ( ( ( ph /\ ps ) /\ ch ) <-> ( ( ch /\ ps ) /\ ph ) ) <-> ( -. ( ( ph /\ ps ) /\ ch ) <-> -. ( ( ch /\ ps ) /\ ph ) ) ) |
3 |
2
|
biimpi |
|- ( ( ( ( ph /\ ps ) /\ ch ) <-> ( ( ch /\ ps ) /\ ph ) ) -> ( -. ( ( ph /\ ps ) /\ ch ) <-> -. ( ( ch /\ ps ) /\ ph ) ) ) |
4 |
1 3
|
ax-mp |
|- ( -. ( ( ph /\ ps ) /\ ch ) <-> -. ( ( ch /\ ps ) /\ ph ) ) |
5 |
4
|
biimpi |
|- ( -. ( ( ph /\ ps ) /\ ch ) -> -. ( ( ch /\ ps ) /\ ph ) ) |