Theorem onss

Description: An ordinal number is a subset of the class of ordinal numbers. (Contributed by NM, 5-Jun-1994)

	Ref	Expression
Assertion	onss	$$⊢A\in \mathrm{On}\to A\subseteq \mathrm{On}$$

Proof

Step	Hyp	Ref	Expression
1		eloni	$$⊢A\in \mathrm{On}\to \mathrm{Ord}A$$
2		ordsson	$$⊢\mathrm{Ord}A\to A\subseteq \mathrm{On}$$
3	1 2	syl	$$⊢A\in \mathrm{On}\to A\subseteq \mathrm{On}$$