Metamath Proof Explorer

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 
|- 1o e. _V

Proof

Step Hyp Ref Expression
1 df1o2 
 |-  1o = { (/) }
2 snex 
 |-  { (/) } e. _V
3 1 2 eqeltri 
 |-  1o e. _V