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Metamath Proof Explorer

Theorem pm5.12

Description: Theorem *5.12 of WhiteheadRussell p. 123. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm5.12 
|- ( ( ph -> ps ) \/ ( ph -> -. ps ) )

Proof

Step Hyp Ref Expression
1 pm2.51 
 |-  ( -. ( ph -> ps ) -> ( ph -> -. ps ) )
2 1 orri 
 |-  ( ( ph -> ps ) \/ ( ph -> -. ps ) )