Theorem cbvsbvf 2397

Description: Change the bound variable (i.e. the substituted one) in wff's linked by implicit substitution. The proof was part of a former cbvabw 2836 version. (Contributed by GG and WL, 26-Oct-2024.)

Hypotheses

Ref	Expression
cbvsbvf.1	⊢ Ⅎ𝑦𝜑
cbvsbvf.2	⊢ Ⅎ𝑥𝜓
cbvsbvf.3	⊢ (𝑥 = 𝑦 → (𝜑 ↔ 𝜓))

Assertion

Ref	Expression
cbvsbvf	⊢ ([𝑧 / 𝑥]𝜑 ↔ [𝑧 / 𝑦]𝜓)

Distinct variable group:   𝑥,𝑦

Allowed substitution hints:   𝜑(𝑥, 𝑦, 𝑧)   𝜓(𝑥, 𝑦, 𝑧)

Proof of Theorem cbvsbvf

Dummy variable 𝑤 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		nfv 1947	. . . . . 6 ⊢ Ⅎ𝑦 𝑥 = 𝑤
2		cbvsbvf.1	. . . . . 6 ⊢ Ⅎ𝑦𝜑
3	1, 2	nfim 1929	. . . . 5 ⊢ Ⅎ𝑦(𝑥 = 𝑤 → 𝜑)
4		nfv 1947	. . . . . 6 ⊢ Ⅎ𝑥 𝑦 = 𝑤
5		cbvsbvf.2	. . . . . 6 ⊢ Ⅎ𝑥𝜓
6	4, 5	nfim 1929	. . . . 5 ⊢ Ⅎ𝑥(𝑦 = 𝑤 → 𝜓)
7		equequ1 2058	. . . . . 6 ⊢ (𝑥 = 𝑦 → (𝑥 = 𝑤 ↔ 𝑦 = 𝑤))
8		cbvsbvf.3	. . . . . 6 ⊢ (𝑥 = 𝑦 → (𝜑 ↔ 𝜓))
9	7, 8	imbi12d 347	. . . . 5 ⊢ (𝑥 = 𝑦 → ((𝑥 = 𝑤 → 𝜑) ↔ (𝑦 = 𝑤 → 𝜓)))
10	3, 6, 9	cbvalv1 2375	. . . 4 ⊢ (∀𝑥(𝑥 = 𝑤 → 𝜑) ↔ ∀𝑦(𝑦 = 𝑤 → 𝜓))
11	10	imbi2i 339	. . 3 ⊢ ((𝑤 = 𝑧 → ∀𝑥(𝑥 = 𝑤 → 𝜑)) ↔ (𝑤 = 𝑧 → ∀𝑦(𝑦 = 𝑤 → 𝜓)))
12	11	albii 1852	. 2 ⊢ (∀𝑤(𝑤 = 𝑧 → ∀𝑥(𝑥 = 𝑤 → 𝜑)) ↔ ∀𝑤(𝑤 = 𝑧 → ∀𝑦(𝑦 = 𝑤 → 𝜓)))
13		dfsb 2101	. 2 ⊢ ([𝑧 / 𝑥]𝜑 ↔ ∀𝑤(𝑤 = 𝑧 → ∀𝑥(𝑥 = 𝑤 → 𝜑)))
14		dfsb 2101	. 2 ⊢ ([𝑧 / 𝑦]𝜓 ↔ ∀𝑤(𝑤 = 𝑧 → ∀𝑦(𝑦 = 𝑤 → 𝜓)))
15	12, 13, 14	3bitr4i 306	1 ⊢ ([𝑧 / 𝑥]𝜑 ↔ [𝑧 / 𝑦]𝜓)

This proof depends on syntax axioms:   → wi 4   ↔ wb 209  ∀wal 1568  Ⅎwnf 1816  [wsb 2099

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1828  ax-4 1842  ax-5 1943  ax-6 2000  ax-7 2041  ax-11 2195  ax-12 2216

This proof depends on definitions:  df-bi 210  df-an 402  df-ex 1813  df-nf 1817  df-sb 2100

This theorem is used by:  cbvabw  2836