Theorem frege56c 44673

Description: Lemma for frege57c 44674. Proposition 56 of [Frege1879] p. 50. (Contributed by RP, 24-Dec-2019.) (Proof modification is discouraged.)

Hypothesis

Ref	Expression
frege56c.b	⊢ 𝐵 ∈ 𝐶

Assertion

Ref	Expression
frege56c	⊢ ((𝐴 = 𝐵 → ([𝐴 / 𝑥]𝜑 → [𝐵 / 𝑥]𝜑)) → (𝐵 = 𝐴 → ([𝐴 / 𝑥]𝜑 → [𝐵 / 𝑥]𝜑)))

Distinct variable groups:   𝑥,𝐴   𝑥,𝐵

Allowed substitution hints:   𝜑(𝑥)   𝐶(𝑥)

Proof of Theorem frege56c

Step	Hyp	Ref	Expression
1		frege56c.b	. . . . 5 ⊢ 𝐵 ∈ 𝐶
2	1	frege54cor1c 44669	. . . 4 ⊢ [𝐵 / 𝑥]𝑥 = 𝐵
3		frege53c 44668	. . . 4 ⊢ ([𝐵 / 𝑥]𝑥 = 𝐵 → (𝐵 = 𝐴 → [𝐴 / 𝑥]𝑥 = 𝐵))
4	2, 3	ax-mp 5	. . 3 ⊢ (𝐵 = 𝐴 → [𝐴 / 𝑥]𝑥 = 𝐵)
5		frege55lem1c 44670	. . 3 ⊢ ((𝐵 = 𝐴 → [𝐴 / 𝑥]𝑥 = 𝐵) → (𝐵 = 𝐴 → 𝐴 = 𝐵))
6	4, 5	ax-mp 5	. 2 ⊢ (𝐵 = 𝐴 → 𝐴 = 𝐵)
7		frege9 44566	. 2 ⊢ ((𝐵 = 𝐴 → 𝐴 = 𝐵) → ((𝐴 = 𝐵 → ([𝐴 / 𝑥]𝜑 → [𝐵 / 𝑥]𝜑)) → (𝐵 = 𝐴 → ([𝐴 / 𝑥]𝜑 → [𝐵 / 𝑥]𝜑))))
8	6, 7	ax-mp 5	1 ⊢ ((𝐴 = 𝐵 → ([𝐴 / 𝑥]𝜑 → [𝐵 / 𝑥]𝜑)) → (𝐵 = 𝐴 → ([𝐴 / 𝑥]𝜑 → [𝐵 / 𝑥]𝜑)))

This proof depends on syntax axioms:   → wi 4   = wceq 1569   ∈ wcel 2142  [wsbc 3743

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1824  ax-4 1838  ax-5 1939  ax-6 1996  ax-7 2037  ax-8 2144  ax-9 2152  ax-ext 2734  ax-frege1 44544  ax-frege2 44545  ax-frege8 44563  ax-frege52c 44642

This proof depends on definitions:  df-bi 210  df-an 401  df-tru 1572  df-ex 1809  df-sb 2096  df-clab 2741  df-cleq 2754  df-clel 2837  df-v 3456  df-sbc 3744  df-sn 4589

This theorem is used by:  frege57c  44674