Theorem 1on

Description: Ordinal 1 is an ordinal number. (Contributed by NM, 29-Oct-1995)

	Ref	Expression
Assertion	1on	$$⊢1_{𝑜}\in \mathrm{On}$$

Proof

Step	Hyp	Ref	Expression
1		df-1o	$$⊢1_{𝑜}=\mathrm{suc}\varnothing$$
2		0elon	$$⊢\varnothing \in \mathrm{On}$$
3	2	onsuci	$$⊢\mathrm{suc}\varnothing \in \mathrm{On}$$
4	1 3	eqeltri	$$⊢1_{𝑜}\in \mathrm{On}$$