Theorem frege26

Description: Identical to idd . Proposition 26 of Frege1879 p. 42. (Contributed by RP, 24-Dec-2019) (Proof modification is discouraged.)

	Ref	Expression
Assertion	frege26	⊢ ( 𝜑 → ( 𝜓 → 𝜓 ) )

Proof

Step	Hyp	Ref	Expression
1		ax-frege1	⊢ ( 𝜓 → ( 𝜑 → 𝜓 ) )
2		ax-frege8	⊢ ( ( 𝜓 → ( 𝜑 → 𝜓 ) ) → ( 𝜑 → ( 𝜓 → 𝜓 ) ) )
3	1 2	ax-mp	⊢ ( 𝜑 → ( 𝜓 → 𝜓 ) )