Theorem snssi

Description: The singleton of an element of a class is a subset of the class. (Contributed by NM, 6-Jun-1994)

	Ref	Expression
Assertion	snssi	$$⊢A\in B\to \left\{A\right\}\subseteq B$$

Proof

Step	Hyp	Ref	Expression
1		snssg	$$⊢A\in B\to \left(A\in B\leftrightarrow \left\{A\right\}\subseteq B\right)$$
2	1	ibi	$$⊢A\in B\to \left\{A\right\}\subseteq B$$