Metamath Proof Explorer

Theorem pm2.51

Description: Theorem *2.51 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm2.51 
|- ( -. ( ph -> ps ) -> ( ph -> -. ps ) )

Proof

Step Hyp Ref Expression
1 conax1k 
 |-  ( -. ( ph -> ps ) -> ( ph -> -. ps ) )