Theorem 5on

Description: Ordinal 5 is an ordinal number. (Contributed by BTernaryTau, 4-Sep-2026)

	Ref	Expression
Assertion	5on	⊢ 5o ∈ On

Proof

Step	Hyp	Ref	Expression
1		df-5o	⊢ 5o = suc 4o
2		4on	⊢ 4o ∈ On
3	2	onsuci	⊢ suc 4o ∈ On
4	1 3	eqeltri	⊢ 5o ∈ On