Theorem nnssz

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

	Ref	Expression
Assertion	nnssz	⊢ ℕ ⊆ ℤ

Proof

Step	Hyp	Ref	Expression
1		nnz	⊢ ( 𝑥 ∈ ℕ → 𝑥 ∈ ℤ )
2	1	ssriv	⊢ ℕ ⊆ ℤ