Theorem unidm

Description: Idempotent law for union of classes. Theorem 23 of Suppes p. 27. (Contributed by NM, 21-Jun-1993)

	Ref	Expression
Assertion	unidm	$$⊢A\cup A=A$$

Proof

Step	Hyp	Ref	Expression
1		oridm	$$⊢\left(x\in A\vee x\in A\right)\leftrightarrow x\in A$$
2	1	uneqri	$$⊢A\cup A=A$$