Theorem frege9 44254

Description: Closed form of syl 17 with swapped antecedents. This proposition differs from frege5 44242 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 44242	. 2 ⊢ ((𝜓 → 𝜒) → ((𝜑 → 𝜓) → (𝜑 → 𝜒)))
2		ax-frege8 44251	. 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 44232  ax-frege2 44233  ax-frege8 44251

This theorem is referenced by:  frege11  44256  frege10  44262  frege19  44266  frege21  44269  frege37  44282  frege56aid  44312  frege56a  44313  frege61a  44321  frege56b  44340  frege61b  44348  frege56c  44361  frege61c  44366  frege117  44422  frege130  44435  frege132  44437