Theorem symdifass 4246

Description: Symmetric difference is associative. (Contributed by Scott Fenton, 24-Apr-2012.) (Proof shortened by BJ, 7-Sep-2022.)

Assertion

Ref	Expression
symdifass	⊢ ((𝐴 △ 𝐵) △ 𝐶) = (𝐴 △ (𝐵 △ 𝐶))

Proof of Theorem symdifass

Dummy variable 𝑥 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		elsymdifxor 4244	. . 3 ⊢ (𝑥 ∈ ((𝐴 △ 𝐵) △ 𝐶) ↔ (𝑥 ∈ (𝐴 △ 𝐵) ⊻ 𝑥 ∈ 𝐶))
2		elsymdifxor 4244	. . . . 5 ⊢ (𝑥 ∈ (𝐴 △ 𝐵) ↔ (𝑥 ∈ 𝐴 ⊻ 𝑥 ∈ 𝐵))
3		biid 261	. . . . 5 ⊢ (𝑥 ∈ 𝐶 ↔ 𝑥 ∈ 𝐶)
4	2, 3	xorbi12i 1517	. . . 4 ⊢ ((𝑥 ∈ (𝐴 △ 𝐵) ⊻ 𝑥 ∈ 𝐶) ↔ ((𝑥 ∈ 𝐴 ⊻ 𝑥 ∈ 𝐵) ⊻ 𝑥 ∈ 𝐶))
5		xorass 1508	. . . 4 ⊢ (((𝑥 ∈ 𝐴 ⊻ 𝑥 ∈ 𝐵) ⊻ 𝑥 ∈ 𝐶) ↔ (𝑥 ∈ 𝐴 ⊻ (𝑥 ∈ 𝐵 ⊻ 𝑥 ∈ 𝐶)))
6		biid 261	. . . . 5 ⊢ (𝑥 ∈ 𝐴 ↔ 𝑥 ∈ 𝐴)
7		elsymdifxor 4244	. . . . . 6 ⊢ (𝑥 ∈ (𝐵 △ 𝐶) ↔ (𝑥 ∈ 𝐵 ⊻ 𝑥 ∈ 𝐶))
8	7	bicomi 223	. . . . 5 ⊢ ((𝑥 ∈ 𝐵 ⊻ 𝑥 ∈ 𝐶) ↔ 𝑥 ∈ (𝐵 △ 𝐶))
9	6, 8	xorbi12i 1517	. . . 4 ⊢ ((𝑥 ∈ 𝐴 ⊻ (𝑥 ∈ 𝐵 ⊻ 𝑥 ∈ 𝐶)) ↔ (𝑥 ∈ 𝐴 ⊻ 𝑥 ∈ (𝐵 △ 𝐶)))
10	4, 5, 9	3bitri 297	. . 3 ⊢ ((𝑥 ∈ (𝐴 △ 𝐵) ⊻ 𝑥 ∈ 𝐶) ↔ (𝑥 ∈ 𝐴 ⊻ 𝑥 ∈ (𝐵 △ 𝐶)))
11		elsymdifxor 4244	. . . 4 ⊢ (𝑥 ∈ (𝐴 △ (𝐵 △ 𝐶)) ↔ (𝑥 ∈ 𝐴 ⊻ 𝑥 ∈ (𝐵 △ 𝐶)))
12	11	bicomi 223	. . 3 ⊢ ((𝑥 ∈ 𝐴 ⊻ 𝑥 ∈ (𝐵 △ 𝐶)) ↔ 𝑥 ∈ (𝐴 △ (𝐵 △ 𝐶)))
13	1, 10, 12	3bitri 297	. 2 ⊢ (𝑥 ∈ ((𝐴 △ 𝐵) △ 𝐶) ↔ 𝑥 ∈ (𝐴 △ (𝐵 △ 𝐶)))
14	13	eqriv 2723	1 ⊢ ((𝐴 △ 𝐵) △ 𝐶) = (𝐴 △ (𝐵 △ 𝐶))

Syntax hints:   ⊻ wxo 1504   = wceq 1533   ∈ wcel 2098   △ csymdif 4236

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1789  ax-4 1803  ax-5 1905  ax-6 1963  ax-7 2003  ax-8 2100  ax-9 2108  ax-ext 2697

This theorem depends on definitions:  df-bi 206  df-an 396  df-or 845  df-xor 1505  df-tru 1536  df-ex 1774  df-sb 2060  df-clab 2704  df-cleq 2718  df-clel 2804  df-v 3470  df-dif 3946  df-un 3948  df-symdif 4237

This theorem is referenced by: (None)