Description: Theorem *4.61 of WhiteheadRussell p. 120. (Contributed by NM, 3-Jan-2005)
Ref | Expression | ||
---|---|---|---|
Assertion | pm4.61 | |- ( -. ( ph -> ps ) <-> ( ph /\ -. ps ) ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | annim | |- ( ( ph /\ -. ps ) <-> -. ( ph -> ps ) ) |
|
2 | 1 | bicomi | |- ( -. ( ph -> ps ) <-> ( ph /\ -. ps ) ) |