Theorem frege9 37126

Description: Closed form of syl 17 with swapped antecedents. This proposition differs from frege5 37114 only in an unessential way. Identical to imim1 81. 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 37114	. 2 ⊢ ((𝜓 → 𝜒) → ((𝜑 → 𝜓) → (𝜑 → 𝜒)))
2		ax-frege8 37123	. 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 37104  ax-frege2 37105  ax-frege8 37123

This theorem is referenced by:  frege11  37128  frege10  37134  frege19  37138  frege21  37141  frege37  37154  frege56aid  37184  frege56a  37185  frege61a  37193  frege56b  37212  frege61b  37220  frege56c  37233  frege61c  37238  frege117  37294  frege130  37307  frege132  37309