Theorem elun1

Description: Membership law for union of classes. (Contributed by NM, 5-Aug-1993)

	Ref	Expression
Assertion	elun1	$$⊢A\in B\to A\in \left(B\cup C\right)$$

Proof

Step	Hyp	Ref	Expression
1		ssun1	$$⊢B\subseteq B\cup C$$
2	1	sseli	$$⊢A\in B\to A\in \left(B\cup C\right)$$