obtain ⟨t1, rfl⟩ := Multiset.exists_cons_of_mem h1
case neg
s : Multiset (ℤ√(-3))
p : ℤ√(-3)
hcoprime : IsCoprime s.prod.re s.prod.im
h1 : p ∈ s
h2 : star p ∈ s
him : ¬p.im = 0
this : star p ≠ p
⊢ IsUnit p
case neg.intro
p : ℤ√(-3)
him : ¬p.im = 0
this : star p ≠ p
t1 : Multiset (ℤ√(-3))
hcoprime : IsCoprime (p ::ₘ t1).prod.re (p ::ₘ t1).prod.im
h1 : p ∈ p ::ₘ t1
h2 : star p ∈ p ::ₘ t1
⊢ IsUnit p