Metamath Proof Explorer

Theorem pm4.25

Description: Theorem *4.25 of WhiteheadRussell p. 117. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm4.25 
|- ( ph <-> ( ph \/ ph ) )

Proof

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