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Metamath Proof Explorer

Theorem 1z

Description: One is an integer. (Contributed by NM, 10-May-2004)

Ref Expression
Assertion 1z 1 ∈ ℤ

Proof

Step Hyp Ref Expression
1 1nn ⊢ 1 ∈ ℕ
2 1 nnzi ⊢ 1 ∈ ℤ