Theorem ssun2

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

	Ref	Expression
Assertion	ssun2	$$⊢A\subseteq B\cup A$$

Proof

Step	Hyp	Ref	Expression
1		ssun1	$$⊢A\subseteq A\cup B$$
2		uncom	$$⊢A\cup B=B\cup A$$
3	1 2	sseqtri	$$⊢A\subseteq B\cup A$$