Theorem frege9 43808

Description: Closed form of syl 17 with swapped antecedents. This proposition differs from frege5 43796 only in an unessential way. Identical to imim1 83. Proposition 9 of [Frege1879] p. 35. (Contributed by RP, 24-Dec-2019.) (Proof modification is discouraged.)

Assertion

Ref	Expression
frege9	⊢ ((𝜑 → 𝜓) → ((𝜓 → 𝜒) → (𝜑 → 𝜒)))

Proof of Theorem frege9

Step	Hyp	Ref	Expression
1		frege5 43796	. 2 ⊢ ((𝜓 → 𝜒) → ((𝜑 → 𝜓) → (𝜑 → 𝜒)))
2		ax-frege8 43805	. 2 ⊢ (((𝜓 → 𝜒) → ((𝜑 → 𝜓) → (𝜑 → 𝜒))) → ((𝜑 → 𝜓) → ((𝜓 → 𝜒) → (𝜑 → 𝜒))))
3	1, 2	ax-mp 5	1 ⊢ ((𝜑 → 𝜓) → ((𝜓 → 𝜒) → (𝜑 → 𝜒)))

Syntax hints:   → wi 4

This theorem was proved from axioms:  ax-mp 5  ax-frege1 43786  ax-frege2 43787  ax-frege8 43805

This theorem is referenced by:  frege11  43810  frege10  43816  frege19  43820  frege21  43823  frege37  43836  frege56aid  43866  frege56a  43867  frege61a  43875  frege56b  43894  frege61b  43902  frege56c  43915  frege61c  43920  frege117  43976  frege130  43989  frege132  43991