Theorem 1oex

Description: Ordinal 1 is a set. (Contributed by BJ, 6-Apr-2019) (Proof shortened by AV, 1-Jul-2022) Remove dependency on ax-10 , ax-11 , ax-12 , ax-un . (Revised by Zhi Wang, 19-Sep-2024)

	Ref	Expression
Assertion	1oex	$$⊢1_{𝑜}\in \mathrm{V}$$

Proof

Step	Hyp	Ref	Expression
1		df1o2	$$⊢1_{𝑜}=\left\{\varnothing \right\}$$
2		snex	$$⊢\left\{\varnothing \right\}\in \mathrm{V}$$
3	1 2	eqeltri	$$⊢1_{𝑜}\in \mathrm{V}$$