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Metamath Proof Explorer

Theorem ssun2

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

		Ref	Expression
	Assertion	ssun2	⊢ 𝐴 ⊆ ( 𝐵 ∪ 𝐴 )

Step	Hyp	Ref	Expression
1		ssun1	⊢ 𝐴 ⊆ ( 𝐴 ∪ 𝐵 )
2		uncom	⊢ ( 𝐴 ∪ 𝐵 ) = ( 𝐵 ∪ 𝐴 )
3	1 2	sseqtri	⊢ 𝐴 ⊆ ( 𝐵 ∪ 𝐴 )