Metamath Proof Explorer

Theorem pm2.6

Description: Theorem *2.6 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm2.6 
|- ( ( -. ph -> ps ) -> ( ( ph -> ps ) -> ps ) )

Proof

Step Hyp Ref Expression
1 id 
 |-  ( ( -. ph -> ps ) -> ( -. ph -> ps ) )
2 idd 
 |-  ( ( -. ph -> ps ) -> ( ps -> ps ) )
3 1 2 jad 
 |-  ( ( -. ph -> ps ) -> ( ( ph -> ps ) -> ps ) )