Theorem 2nn

Description: 2 is a positive integer. (Contributed by NM, 20-Aug-2001)

	Ref	Expression
Assertion	2nn	$$⊢2\in \mathbb{N}$$

Proof

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