∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] [inst_1 : CategoryTheory.Preadditive C]
  {F G K : CochainComplex C ℤ} {n : ℤ} (z : CochainComplex.HomComplex.Cocycle F G n) (f : G ⟶ K),
  ↑(z.postcomp f) = (↑z).comp (CochainComplex.HomComplex.Cochain.ofHom f) ⋯