Metamath Proof Explorer


Theorem frege26

Description: Identical to idd . Proposition 26 of Frege1879 p. 42. (Contributed by RP, 24-Dec-2019) (Proof modification is discouraged.)

Ref Expression
Assertion frege26 φ ψ ψ

Proof

Step Hyp Ref Expression
1 ax-frege1 ψ φ ψ
2 ax-frege8 ψ φ ψ φ ψ ψ
3 1 2 ax-mp φ ψ ψ