Theorem bnj1213

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

	Ref	Expression
Hypotheses	bnj1213.1	$$⊢A\subseteq B$$
	bnj1213.2	$$⊢\theta \to x\in A$$
Assertion	bnj1213	$$⊢\theta \to x\in B$$

Proof

Step	Hyp	Ref	Expression
1		bnj1213.1	$$⊢A\subseteq B$$
2		bnj1213.2	$$⊢\theta \to x\in A$$
3	1 2	sselid	$$⊢\theta \to x\in B$$