Theorem unidm 3408

Description: Idempotent law for union of classes. Theorem 23 of [Suppes] p. 27. (Contributed by NM, 5-Aug-1993.)

Assertion

Ref	Expression
unidm	⊢ (A ∪ A) = A

Proof of Theorem unidm

Dummy variable x is distinct from all other variables.

Step	Hyp	Ref	Expression
1		oridm 500	. 2 ⊢ ((x ∈ A ∨ x ∈ A) ↔ x ∈ A)
2	1	uneqri 3407	1 ⊢ (A ∪ A) = A

Syntax hints:   = wceq 1642   ∈ wcel 1710   ∪ cun 3208

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-6 1729  ax-7 1734  ax-11 1746  ax-12 1925  ax-ext 2334

This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-nan 1288  df-tru 1319  df-ex 1542  df-nf 1545  df-sb 1649  df-clab 2340  df-cleq 2346  df-clel 2349  df-nfc 2479  df-v 2862  df-nin 3212  df-compl 3213  df-un 3215

This theorem is referenced by:  unundi  3425  unundir  3426  uneqin  3507  difabs  3519  undifabs  3628  dfif5  3675  dfsn2  3748  diftpsn3  3850  unisn  3908