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 C_ B
	bnj1213.2	|- ( th -> x e. A )
Assertion	bnj1213	|- ( th -> x e. B )

Proof

Step	Hyp	Ref	Expression
1		bnj1213.1	|- A C_ B
2		bnj1213.2	|- ( th -> x e. A )
3	1 2	sseldi	|- ( th -> x e. B )