refine' ⟨u, _, _⟩
case intro
z : ℤ√(-3)
h : IsUnit z
u : ℤˣ
hu : z = ↑↑u
⊢ ∃ u, z = ↑u ∧ |u| = 1
case intro.refine'_1
z : ℤ√(-3)
h : IsUnit z
u : ℤˣ
hu : z = ↑↑u
⊢ z = ↑↑u

case intro.refine'_2
z : ℤ√(-3)
h : IsUnit z
u : ℤˣ
hu : z = ↑↑u
⊢ |↑u| = 1