Theorem snssd

Description: The singleton of an element of a class is a subset of the class (deduction form). (Contributed by Jonathan Ben-Naim, 3-Jun-2011)

	Ref	Expression
Hypothesis	snssd.1	|- ( ph -> A e. B )
Assertion	snssd	|- ( ph -> { A } C_ B )

Proof

Step	Hyp	Ref	Expression
1		snssd.1	|- ( ph -> A e. B )
2		snssi	|- ( A e. B -> { A } C_ B )
3	1 2	syl	|- ( ph -> { A } C_ B )