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Metamath Proof Explorer

Theorem pm2.53

Description: Theorem *2.53 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm2.53 
|- ( ( ph \/ ps ) -> ( -. ph -> ps ) )

Proof

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