Theorem 1onOLD

Description: Obsolete version of 1on as of 30-Nov-2024. (Contributed by NM, 29-Oct-1995) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	1onOLD	⊢ 1o ∈ On

Proof

Step	Hyp	Ref	Expression
1		df-1o	⊢ 1o = suc ∅
2		0elon	⊢ ∅ ∈ On
3	2	onsuci	⊢ suc ∅ ∈ On
4	1 3	eqeltri	⊢ 1o ∈ On