Theorem elun2

Description: Membership law for union of classes. (Contributed by NM, 30-Aug-1993)

	Ref	Expression
Assertion	elun2	⊢ ( 𝐴 ∈ 𝐵 → 𝐴 ∈ ( 𝐶 ∪ 𝐵 ) )

Proof

Step	Hyp	Ref	Expression
1		ssun2	⊢ 𝐵 ⊆ ( 𝐶 ∪ 𝐵 )
2	1	sseli	⊢ ( 𝐴 ∈ 𝐵 → 𝐴 ∈ ( 𝐶 ∪ 𝐵 ) )