Theorem nnssz

Description: Positive integers are a subset of integers. (Contributed by NM, 9-Jan-2002)

	Ref	Expression
Assertion	nnssz	$$⊢\mathbb{N}\subseteq \mathbb{Z}$$

Proof

Step	Hyp	Ref	Expression
1		nnz	$$⊢x\in \mathbb{N}\to x\in \mathbb{Z}$$
2	1	ssriv	$$⊢\mathbb{N}\subseteq \mathbb{Z}$$