Metamath Proof Explorer

Theorem 6on

Description: Ordinal 6 is an ordinal number. (Contributed by BTernaryTau, 4-Sep-2026)

Ref Expression
Assertion 6on 
|- 6o e. On

Proof

Step Hyp Ref Expression
1 df-6o 
 |-  6o = suc 5o
2 5on 
 |-  5o e. On
3 2 onsuci 
 |-  suc 5o e. On
4 1 3 eqeltri 
 |-  6o e. On