obtain ⟨v, hv⟩ : IsUnit z.re := by rwa [Int.isUnit_iff_abs_eq]
case intro
z : ℤ√(-3)
h : IsUnit z
u : |z.re| = 1
hu : z.im = 0
⊢ ∃ u, z = ↑↑u
case intro.intro
z : ℤ√(-3)
h : IsUnit z
u : |z.re| = 1
hu : z.im = 0
v : ℤˣ
hv : ↑v = z.re
⊢ ∃ u, z = ↑↑u