Theorem onssi

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

	Ref	Expression
Hypothesis	onssi.1	$$⊢A\in \mathrm{On}$$
Assertion	onssi	$$⊢A\subseteq \mathrm{On}$$

Proof

Step	Hyp	Ref	Expression
1		onssi.1	$$⊢A\in \mathrm{On}$$
2		onss	$$⊢A\in \mathrm{On}\to A\subseteq \mathrm{On}$$
3	1 2	ax-mp	$$⊢A\subseteq \mathrm{On}$$