Theorem nnzi

Description: A positive integer is an integer. (Contributed by Mario Carneiro, 18-Feb-2014)

	Ref	Expression
Hypothesis	nnzi.1	$$⊢N\in \mathbb{N}$$
Assertion	nnzi	$$⊢N\in \mathbb{Z}$$

Proof

Step	Hyp	Ref	Expression
1		nnzi.1	$$⊢N\in \mathbb{N}$$
2		nnssz	$$⊢\mathbb{N}\subseteq \mathbb{Z}$$
3	2 1	sselii	$$⊢N\in \mathbb{Z}$$