Theorem symdifass 4214

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 4212	. . 3 ⊢ (𝑥 ∈ ((𝐴 △ 𝐵) △ 𝐶) ↔ (𝑥 ∈ (𝐴 △ 𝐵) ⊻ 𝑥 ∈ 𝐶))
2		elsymdifxor 4212	. . . . 5 ⊢ (𝑥 ∈ (𝐴 △ 𝐵) ↔ (𝑥 ∈ 𝐴 ⊻ 𝑥 ∈ 𝐵))
3		biid 264	. . . . 5 ⊢ (𝑥 ∈ 𝐶 ↔ 𝑥 ∈ 𝐶)
4	2, 3	xorbi12i 1552	. . . 4 ⊢ ((𝑥 ∈ (𝐴 △ 𝐵) ⊻ 𝑥 ∈ 𝐶) ↔ ((𝑥 ∈ 𝐴 ⊻ 𝑥 ∈ 𝐵) ⊻ 𝑥 ∈ 𝐶))
5		xorass 1543	. . . 4 ⊢ (((𝑥 ∈ 𝐴 ⊻ 𝑥 ∈ 𝐵) ⊻ 𝑥 ∈ 𝐶) ↔ (𝑥 ∈ 𝐴 ⊻ (𝑥 ∈ 𝐵 ⊻ 𝑥 ∈ 𝐶)))
6		biid 264	. . . . 5 ⊢ (𝑥 ∈ 𝐴 ↔ 𝑥 ∈ 𝐴)
7		elsymdifxor 4212	. . . . . 6 ⊢ (𝑥 ∈ (𝐵 △ 𝐶) ↔ (𝑥 ∈ 𝐵 ⊻ 𝑥 ∈ 𝐶))
8	7	bicomi 227	. . . . 5 ⊢ ((𝑥 ∈ 𝐵 ⊻ 𝑥 ∈ 𝐶) ↔ 𝑥 ∈ (𝐵 △ 𝐶))
9	6, 8	xorbi12i 1552	. . . 4 ⊢ ((𝑥 ∈ 𝐴 ⊻ (𝑥 ∈ 𝐵 ⊻ 𝑥 ∈ 𝐶)) ↔ (𝑥 ∈ 𝐴 ⊻ 𝑥 ∈ (𝐵 △ 𝐶)))
10	4, 5, 9	3bitri 300	. . 3 ⊢ ((𝑥 ∈ (𝐴 △ 𝐵) ⊻ 𝑥 ∈ 𝐶) ↔ (𝑥 ∈ 𝐴 ⊻ 𝑥 ∈ (𝐵 △ 𝐶)))
11		elsymdifxor 4212	. . . 4 ⊢ (𝑥 ∈ (𝐴 △ (𝐵 △ 𝐶)) ↔ (𝑥 ∈ 𝐴 ⊻ 𝑥 ∈ (𝐵 △ 𝐶)))
12	11	bicomi 227	. . 3 ⊢ ((𝑥 ∈ 𝐴 ⊻ 𝑥 ∈ (𝐵 △ 𝐶)) ↔ 𝑥 ∈ (𝐴 △ (𝐵 △ 𝐶)))
13	1, 10, 12	3bitri 300	. 2 ⊢ (𝑥 ∈ ((𝐴 △ 𝐵) △ 𝐶) ↔ 𝑥 ∈ (𝐴 △ (𝐵 △ 𝐶)))
14	13	eqriv 2758	1 ⊢ ((𝐴 △ 𝐵) △ 𝐶) = (𝐴 △ (𝐵 △ 𝐶))

Syntax hints:   ⊻ wxo 1539   = wceq 1568   ∈ wcel 2141   △ csymdif 4204

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1823  ax-4 1837  ax-5 1938  ax-6 1995  ax-7 2036  ax-8 2143  ax-9 2151  ax-ext 2733

This theorem depends on definitions:  df-bi 210  df-an 401  df-or 861  df-xor 1540  df-tru 1571  df-ex 1808  df-sb 2095  df-clab 2740  df-cleq 2753  df-clel 2836  df-v 3455  df-dif 3907  df-un 3909  df-symdif 4205

This theorem is referenced by: (None)