Theorem 3nn

Description: 3 is a positive integer. (Contributed by NM, 8-Jan-2006)

	Ref	Expression
Assertion	3nn	$$⊢3\in \mathbb{N}$$

Proof

Step	Hyp	Ref	Expression
1		df-3	$$⊢3=2+1$$
2		2nn	$$⊢2\in \mathbb{N}$$
3		peano2nn	$$⊢2\in \mathbb{N}\to 2+1\in \mathbb{N}$$
4	2 3	ax-mp	$$⊢2+1\in \mathbb{N}$$
5	1 4	eqeltri	$$⊢3\in \mathbb{N}$$