Description: Theorem *4.56 of WhiteheadRussell p. 120. (Contributed by NM, 3-Jan-2005)
Ref | Expression | ||
---|---|---|---|
Assertion | pm4.56 | |- ( ( -. ph /\ -. ps ) <-> -. ( ph \/ ps ) ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | ioran | |- ( -. ( ph \/ ps ) <-> ( -. ph /\ -. ps ) ) |
|
2 | 1 | bicomi | |- ( ( -. ph /\ -. ps ) <-> -. ( ph \/ ps ) ) |