have : Even (evenFactorExp r) :=
  by
  suffices Even (3 * evenFactorExp r)
    by
    rw [Nat.even_mul] at this
    apply this.resolve_left
    norm_num
  rw [← evenFactorExp.pow r 3, hcube]
  exact factors_2_even' hcoprime
case h.e'_4
a : ℤ√(-3)
r : ℤ
hcoprime : IsCoprime a.re a.im
hcube : r ^ 3 = Zsqrtd.norm a
f : Multiset (ℤ√(-3)) := factorization' hcoprime
h1 : a = Multiset.prod f ∨ a = -Multiset.prod f
h2 : ∀ (pq : ℤ√(-3)), pq ∈ f → 0 ≤ pq.re ∧ pq.im ≠ 0 ∧ OddPrimeOrFour (Zsqrtd.norm pq)
hf : f = factorization' hcoprime
x : ℤ√(-3)
hx : x ∈ f
⊢ Multiset.count x f = 3 * Multiset.count (Zsqrtd.norm x) (factorsOddPrimeOrFour r)
case h.e'_4
a : ℤ√(-3)
r : ℤ
hcoprime : IsCoprime a.re a.im
hcube : r ^ 3 = Zsqrtd.norm a
f : Multiset (ℤ√(-3)) := factorization' hcoprime
h1 : a = Multiset.prod f ∨ a = -Multiset.prod f
h2 : ∀ (pq : ℤ√(-3)), pq ∈ f → 0 ≤ pq.re ∧ pq.im ≠ 0 ∧ OddPrimeOrFour (Zsqrtd.norm pq)
hf : f = factorization' hcoprime
x : ℤ√(-3)
hx : x ∈ f
this : Even (evenFactorExp r)
⊢ Multiset.count x f = 3 * Multiset.count (Zsqrtd.norm x) (factorsOddPrimeOrFour r)