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Metamath Proof Explorer

Theorem pm4.66

Description: Theorem *4.66 of WhiteheadRussell p. 120. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm4.66 
|- ( ( -. ph -> -. ps ) <-> ( ph \/ -. ps ) )

Proof

Step Hyp Ref Expression
1 pm4.64 
 |-  ( ( -. ph -> -. ps ) <-> ( ph \/ -. ps ) )