Theorem 2on

Description: Ordinal 2 is an ordinal number. (Contributed by NM, 18-Feb-2004) (Proof shortened by Andrew Salmon, 12-Aug-2011)

	Ref	Expression
Assertion	2on	⊢ 2o ∈ On

Proof

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