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Metamath Proof Explorer

Theorem pm4.67

Description: Theorem *4.67 of WhiteheadRussell p. 120. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm4.67 
|- ( -. ( -. ph -> -. ps ) <-> ( -. ph /\ ps ) )

Proof

Step Hyp Ref Expression
1 pm4.63 
 |-  ( -. ( -. ph -> -. ps ) <-> ( -. ph /\ ps ) )