∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.Preadditive C]
  (F G : CochainComplex C ℤ) (x x_1 x_2 : ℤ),
  CategoryTheory.CategoryStruct.comp (AddCommGrpCat.ofHom ↑(CochainComplex.HomComplex.δ_hom ℤ F G x x_1))
      (AddCommGrpCat.ofHom ↑(CochainComplex.HomComplex.δ_hom ℤ F G x_1 x_2)) =
    0