Metamath Proof Explorer

Theorem pm2.52

Description: Theorem *2.52 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005) (Proof shortened by Wolf Lammen, 8-Oct-2012)

Ref Expression
Assertion pm2.52 
|- ( -. ( ph -> ps ) -> ( -. ph -> -. ps ) )

Proof

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