Theorem bnj931

Description: First-order logic and set theory. (Contributed by Jonathan Ben-Naim, 3-Jun-2011) (New usage is discouraged.)

	Ref	Expression
Hypothesis	bnj931.1	$$⊢A=B\cup C$$
Assertion	bnj931	$$⊢B\subseteq A$$

Proof

Step	Hyp	Ref	Expression
1		bnj931.1	$$⊢A=B\cup C$$
2		ssun1	$$⊢B\subseteq B\cup C$$
3	2 1	sseqtrri	$$⊢B\subseteq A$$