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 ∈ 𝐵 → { 𝐴 } ⊆ 𝐵 )

Proof

Step	Hyp	Ref	Expression
1		snssg	⊢ ( 𝐴 ∈ 𝐵 → ( 𝐴 ∈ 𝐵 ↔ { 𝐴 } ⊆ 𝐵 ) )
2	1	ibi	⊢ ( 𝐴 ∈ 𝐵 → { 𝐴 } ⊆ 𝐵 )