Theorem onssi

Description: An ordinal number is a subset of On . (Contributed by NM, 11-Aug-1994)

	Ref	Expression
Hypothesis	onssi.1	⊢ 𝐴 ∈ On
Assertion	onssi	⊢ 𝐴 ⊆ On

Proof

Step	Hyp	Ref	Expression
1		onssi.1	⊢ 𝐴 ∈ On
2		onss	⊢ ( 𝐴 ∈ On → 𝐴 ⊆ On )
3	1 2	ax-mp	⊢ 𝐴 ⊆ On