Theorem frege26 44809

Description: Identical to idd 25. Proposition 26 of [Frege1879] p. 42. (Contributed by RP, 24-Dec-2019.) (Proof modification is discouraged.)

Assertion

Ref	Expression
frege26	⊢ (𝜑 → (𝜓 → 𝜓))

Proof of Theorem frege26

Step	Hyp	Ref	Expression
1		ax-frege1 44789	. 2 ⊢ (𝜓 → (𝜑 → 𝜓))
2		ax-frege8 44808	. 2 ⊢ ((𝜓 → (𝜑 → 𝜓)) → (𝜑 → (𝜓 → 𝜓)))
3	1, 2	ax-mp 5	1 ⊢ (𝜑 → (𝜓 → 𝜓))

This proof depends on syntax axioms:   → wi 4

This proof depends on axioms:  ax-mp 5  ax-frege1 44789  ax-frege8 44808

This theorem is used by:  frege27  44810