Metamath Proof Explorer

Theorem 7on

Description: Ordinal 7 is an ordinal number. (Contributed by BTernaryTau, 4-Sep-2026)

Ref Expression
Assertion 7on 
|- 7o e. On

Proof

Step Hyp Ref Expression
1 df-7o 
 |-  7o = suc 6o
2 6on 
 |-  6o e. On
3 2 onsuci 
 |-  suc 6o e. On
4 1 3 eqeltri 
 |-  7o e. On