Theorem frege9 43214

Description: Closed form of syl 17 with swapped antecedents. This proposition differs from frege5 43202 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 43202	. 2 ⊢ ((𝜓 → 𝜒) → ((𝜑 → 𝜓) → (𝜑 → 𝜒)))
2		ax-frege8 43211	. 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 43192  ax-frege2 43193  ax-frege8 43211

This theorem is referenced by:  frege11  43216  frege10  43222  frege19  43226  frege21  43229  frege37  43242  frege56aid  43272  frege56a  43273  frege61a  43281  frege56b  43300  frege61b  43308  frege56c  43321  frege61c  43326  frege117  43382  frege130  43395  frege132  43397