have mul_ident := Impl.multiplication.mul_identity (ℕ := ℕ)
x : ℤ
⊢ Positive x ↔ ∃ n, Positive n ∧ x ≃ coe n
x : ℤ
mul_ident : AA.Identity (coe 1) fun x x_1 => x * x_1
⊢ Positive x ↔ ∃ n, Positive n ∧ x ≃ coe n