have : star p ∈ t1 := by
  rw [Multiset.mem_cons] at h2
  exact h2.resolve_left this
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
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
this : star p ∈ t1
⊢ IsUnit p