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Metamath Proof Explorer

Theorem elun1

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

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

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