Theorem frege53c 41522

Description: Proposition 53 of [Frege1879] p. 50. (Contributed by RP, 24-Dec-2019.) (Proof modification is discouraged.)

Assertion

Ref	Expression
frege53c	⊢ ([𝐴 / 𝑥]𝜑 → (𝐴 = 𝐵 → [𝐵 / 𝑥]𝜑))

Proof of Theorem frege53c

Step	Hyp	Ref	Expression
1		ax-frege52c 41496	. 2 ⊢ (𝐴 = 𝐵 → ([𝐴 / 𝑥]𝜑 → [𝐵 / 𝑥]𝜑))
2		ax-frege8 41417	. 2 ⊢ ((𝐴 = 𝐵 → ([𝐴 / 𝑥]𝜑 → [𝐵 / 𝑥]𝜑)) → ([𝐴 / 𝑥]𝜑 → (𝐴 = 𝐵 → [𝐵 / 𝑥]𝜑)))
3	1, 2	ax-mp 5	1 ⊢ ([𝐴 / 𝑥]𝜑 → (𝐴 = 𝐵 → [𝐵 / 𝑥]𝜑))

Syntax hints:   → wi 4   = wceq 1539  [wsbc 3716

This theorem was proved from axioms:  ax-mp 5  ax-frege8 41417  ax-frege52c 41496

This theorem is referenced by:  frege55lem2c  41525  frege55c  41526  frege56c  41527  frege92  41563