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 ¬ φ φ ψ

Proof

Step Hyp Ref Expression
1 frege36 φ ¬ φ ψ
2 ax-frege8 φ ¬ φ ψ ¬ φ φ ψ
3 1 2 ax-mp ¬ φ φ ψ