Metamath Proof Explorer


Theorem frege24

Description: Closed form for a1d . Deduction introducing an embedded antecedent. Identical to rp-frege24 which was proved without relying on ax-frege8 . Proposition 24 of Frege1879 p. 42. (Contributed by RP, 24-Dec-2019) (Proof modification is discouraged.)

Ref Expression
Assertion frege24 φψφχψ

Proof

Step Hyp Ref Expression
1 ax-frege1 φψχφψ
2 frege12 φψχφψφψφχψ
3 1 2 ax-mp φψφχψ