convert (add_zero
  (Multiset.filter (fun a => 2 = a ∨ Odd a) (UniqueFactorizationMonoid.normalizedFactors x))).symm
case neg
x : ℤ
hx : ¬x = 0
⊢ UniqueFactorizationMonoid.normalizedFactors x =
    Multiset.filter (fun a => 2 = a ∨ Odd a) (UniqueFactorizationMonoid.normalizedFactors x) +
      Multiset.filter (fun a => 2 = a ∧ Odd a) (UniqueFactorizationMonoid.normalizedFactors x)
case h.e'_2
x : ℤ
hx : ¬x = 0
⊢ UniqueFactorizationMonoid.normalizedFactors x =
    Multiset.filter (fun a => 2 = a ∨ Odd a) (UniqueFactorizationMonoid.normalizedFactors x)

case h.e'_3.h.e'_6
x : ℤ
hx : ¬x = 0
⊢ Multiset.filter (fun a => 2 = a ∧ Odd a) (UniqueFactorizationMonoid.normalizedFactors x) = 0