obtain ⟨v, hv1, hv2⟩ := Zsqrt3.coe_of_isUnit' u.isUnit
case intro
x A : ℤ√(-3)
hx : x.re = 0
u : (ℤ√(-3))ˣ
hu : x * ↑u = A
⊢ x = A ∨ x = star A
case intro.intro.intro
x A : ℤ√(-3)
hx : x.re = 0
u : (ℤ√(-3))ˣ
hu : x * ↑u = A
v : ℤ
hv1 : ↑u = ↑v
hv2 : |v| = 1
⊢ x = A ∨ x = star A