Metamath Proof Explorer

Theorem pm4.64

Description: Theorem *4.64 of WhiteheadRussell p. 120. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm4.64 
|- ( ( -. ph -> ps ) <-> ( ph \/ ps ) )

Proof

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