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Metamath Proof Explorer

Theorem pm2.68

Description: Theorem *2.68 of WhiteheadRussell p. 108. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm2.68 
|- ( ( ( ph -> ps ) -> ps ) -> ( ph \/ ps ) )

Proof

Step Hyp Ref Expression
1 jarl 
 |-  ( ( ( ph -> ps ) -> ps ) -> ( -. ph -> ps ) )
2 1 orrd 
 |-  ( ( ( ph -> ps ) -> ps ) -> ( ph \/ ps ) )