Theorem frege9 44089

Description: Closed form of syl 17 with swapped antecedents. This proposition differs from frege5 44077 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 44077	. 2 ⊢ ((𝜓 → 𝜒) → ((𝜑 → 𝜓) → (𝜑 → 𝜒)))
2		ax-frege8 44086	. 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 44067  ax-frege2 44068  ax-frege8 44086

This theorem is referenced by:  frege11  44091  frege10  44097  frege19  44101  frege21  44104  frege37  44117  frege56aid  44147  frege56a  44148  frege61a  44156  frege56b  44175  frege61b  44183  frege56c  44196  frege61c  44201  frege117  44257  frege130  44270  frege132  44272