Theorem 3on

Description: Ordinal 3 is an ordinal number. (Contributed by Mario Carneiro, 5-Jan-2016)

	Ref	Expression
Assertion	3on	⊢ 3o ∈ On

Proof

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