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