Theorem 4on

Description: Ordinal 4 is an ordinal number. (Contributed by Mario Carneiro, 5-Jan-2016)

	Ref	Expression
Assertion	4on	⊢ 4o ∈ On

Proof

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