Theorem csbgfi 3871

Description: Substitution for a variable not free in a class does not affect it, in inference form. (Contributed by Giovanni Mascellani, 4-Jun-2019.)

Hypotheses

Ref	Expression
csbgfi.1	⊢ 𝐴 ∈ V
csbgfi.2	⊢ Ⅎ𝑥𝐵

Assertion

Ref	Expression
csbgfi	⊢ ⦋𝐴 / 𝑥⦌𝐵 = 𝐵

Proof of Theorem csbgfi

Dummy variable 𝑦 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		df-csb 3852	. . . 4 ⊢ ⦋𝐴 / 𝑥⦌𝐵 = {𝑦 ∣ [𝐴 / 𝑥]𝑦 ∈ 𝐵}
2	1	eqabri 2879	. . 3 ⊢ (𝑦 ∈ ⦋𝐴 / 𝑥⦌𝐵 ↔ [𝐴 / 𝑥]𝑦 ∈ 𝐵)
3		csbgfi.1	. . . 4 ⊢ 𝐴 ∈ V
4		csbgfi.2	. . . . 5 ⊢ Ⅎ𝑥𝐵
5	4	nfcri 2891	. . . 4 ⊢ Ⅎ𝑥 𝑦 ∈ 𝐵
6	3, 5	sbcgfi 3816	. . 3 ⊢ ([𝐴 / 𝑥]𝑦 ∈ 𝐵 ↔ 𝑦 ∈ 𝐵)
7	2, 6	bitri 275	. 2 ⊢ (𝑦 ∈ ⦋𝐴 / 𝑥⦌𝐵 ↔ 𝑦 ∈ 𝐵)
8	7	eqriv 2734	1 ⊢ ⦋𝐴 / 𝑥⦌𝐵 = 𝐵

Syntax hints:   = wceq 1542   ∈ wcel 2114  Ⅎwnfc 2884  Vcvv 3442  [wsbc 3742  ⦋csb 3851

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1797  ax-4 1811  ax-5 1912  ax-6 1969  ax-7 2010  ax-8 2116  ax-9 2124  ax-12 2185  ax-ext 2709

This theorem depends on definitions:  df-bi 207  df-an 396  df-tru 1545  df-ex 1782  df-nf 1786  df-sb 2069  df-clab 2716  df-cleq 2729  df-clel 2812  df-nfc 2886  df-sbc 3743  df-csb 3852

This theorem is referenced by:  fmptdF  32745  sbccom2f  38371  evl1gprodd  42481