Metamath Proof Explorer

Theorem frege38

Description: Identical to pm2.21 . Proposition 38 of Frege1879 p. 46. (Contributed by RP, 24-Dec-2019) (Proof modification is discouraged.)

Ref Expression
Assertion frege38 
|- ( -. ph -> ( ph -> ps ) )

Proof

Step Hyp Ref Expression
1 frege36 
 |-  ( ph -> ( -. ph -> ps ) )
2 ax-frege8 
 |-  ( ( ph -> ( -. ph -> ps ) ) -> ( -. ph -> ( ph -> ps ) ) )
3 1 2 ax-mp 
 |-  ( -. ph -> ( ph -> ps ) )