Metamath Proof Explorer

Theorem pm4.56

Description: Theorem *4.56 of WhiteheadRussell p. 120. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm4.56 
|- ( ( -. ph /\ -. ps ) <-> -. ( ph \/ ps ) )

Proof

Step Hyp Ref Expression
1 ioran 
 |-  ( -. ( ph \/ ps ) <-> ( -. ph /\ -. ps ) )
2 1 bicomi 
 |-  ( ( -. ph /\ -. ps ) <-> -. ( ph \/ ps ) )