Theorem sbccom2f 38133

Description: Commutative law for double class substitution, with nonfree variable condition. (Contributed by Giovanni Mascellani, 31-May-2019.)

Hypotheses

Ref	Expression
sbccom2f.1	⊢ 𝐴 ∈ V
sbccom2f.2	⊢ Ⅎ𝑦𝐴

Assertion

Ref	Expression
sbccom2f	⊢ ([𝐴 / 𝑥][𝐵 / 𝑦]𝜑 ↔ [⦋𝐴 / 𝑥⦌𝐵 / 𝑦][𝐴 / 𝑥]𝜑)

Distinct variable group:   𝑥,𝑦

Allowed substitution hints:   𝜑(𝑥,𝑦)   𝐴(𝑥,𝑦)   𝐵(𝑥,𝑦)

Proof of Theorem sbccom2f

Dummy variable 𝑧 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		sbccow 3811	. . . 4 ⊢ ([𝐵 / 𝑧][𝑧 / 𝑦]𝜑 ↔ [𝐵 / 𝑦]𝜑)
2	1	bicomi 224	. . 3 ⊢ ([𝐵 / 𝑦]𝜑 ↔ [𝐵 / 𝑧][𝑧 / 𝑦]𝜑)
3	2	sbcbii 3846	. 2 ⊢ ([𝐴 / 𝑥][𝐵 / 𝑦]𝜑 ↔ [𝐴 / 𝑥][𝐵 / 𝑧][𝑧 / 𝑦]𝜑)
4		sbccom2f.1	. . 3 ⊢ 𝐴 ∈ V
5	4	sbccom2 38132	. 2 ⊢ ([𝐴 / 𝑥][𝐵 / 𝑧][𝑧 / 𝑦]𝜑 ↔ [⦋𝐴 / 𝑥⦌𝐵 / 𝑧][𝐴 / 𝑥][𝑧 / 𝑦]𝜑)
6		vex 3484	. . . . . . 7 ⊢ 𝑧 ∈ V
7	6	sbccom2 38132	. . . . . 6 ⊢ ([𝑧 / 𝑦][𝐴 / 𝑥]𝜑 ↔ [⦋𝑧 / 𝑦⦌𝐴 / 𝑥][𝑧 / 𝑦]𝜑)
8		sbccom2f.2	. . . . . . . 8 ⊢ Ⅎ𝑦𝐴
9	6, 8	csbgfi 3919	. . . . . . 7 ⊢ ⦋𝑧 / 𝑦⦌𝐴 = 𝐴
10		dfsbcq 3790	. . . . . . 7 ⊢ (⦋𝑧 / 𝑦⦌𝐴 = 𝐴 → ([⦋𝑧 / 𝑦⦌𝐴 / 𝑥][𝑧 / 𝑦]𝜑 ↔ [𝐴 / 𝑥][𝑧 / 𝑦]𝜑))
11	9, 10	ax-mp 5	. . . . . 6 ⊢ ([⦋𝑧 / 𝑦⦌𝐴 / 𝑥][𝑧 / 𝑦]𝜑 ↔ [𝐴 / 𝑥][𝑧 / 𝑦]𝜑)
12	7, 11	bitri 275	. . . . 5 ⊢ ([𝑧 / 𝑦][𝐴 / 𝑥]𝜑 ↔ [𝐴 / 𝑥][𝑧 / 𝑦]𝜑)
13	12	bicomi 224	. . . 4 ⊢ ([𝐴 / 𝑥][𝑧 / 𝑦]𝜑 ↔ [𝑧 / 𝑦][𝐴 / 𝑥]𝜑)
14	13	sbcbii 3846	. . 3 ⊢ ([⦋𝐴 / 𝑥⦌𝐵 / 𝑧][𝐴 / 𝑥][𝑧 / 𝑦]𝜑 ↔ [⦋𝐴 / 𝑥⦌𝐵 / 𝑧][𝑧 / 𝑦][𝐴 / 𝑥]𝜑)
15		sbccow 3811	. . 3 ⊢ ([⦋𝐴 / 𝑥⦌𝐵 / 𝑧][𝑧 / 𝑦][𝐴 / 𝑥]𝜑 ↔ [⦋𝐴 / 𝑥⦌𝐵 / 𝑦][𝐴 / 𝑥]𝜑)
16	14, 15	bitri 275	. 2 ⊢ ([⦋𝐴 / 𝑥⦌𝐵 / 𝑧][𝐴 / 𝑥][𝑧 / 𝑦]𝜑 ↔ [⦋𝐴 / 𝑥⦌𝐵 / 𝑦][𝐴 / 𝑥]𝜑)
17	3, 5, 16	3bitri 297	1 ⊢ ([𝐴 / 𝑥][𝐵 / 𝑦]𝜑 ↔ [⦋𝐴 / 𝑥⦌𝐵 / 𝑦][𝐴 / 𝑥]𝜑)

Syntax hints:   ↔ wb 206   = wceq 1540   ∈ wcel 2108  Ⅎwnfc 2890  Vcvv 3480  [wsbc 3788  ⦋csb 3899

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1795  ax-4 1809  ax-5 1910  ax-6 1967  ax-7 2007  ax-8 2110  ax-9 2118  ax-10 2141  ax-11 2157  ax-12 2177  ax-ext 2708

This theorem depends on definitions:  df-bi 207  df-an 396  df-or 849  df-tru 1543  df-ex 1780  df-nf 1784  df-sb 2065  df-clab 2715  df-cleq 2729  df-clel 2816  df-nfc 2892  df-v 3482  df-sbc 3789  df-csb 3900

This theorem is referenced by:  sbccom2fi  38134