Metamath Proof Explorer

Theorem pm4.63

Description: Theorem *4.63 of WhiteheadRussell p. 120. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm4.63 
|- ( -. ( ph -> -. ps ) <-> ( ph /\ ps ) )

Proof

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