∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.Preadditive C] {X : C}
  {K : CochainComplex C ℤ} {p : ℤ} (f g : K.X p ⟶ X) (p' : ℤ),
  CategoryTheory.CategoryStruct.comp (K.d p' p) f = 0 →
    CategoryTheory.CategoryStruct.comp (K.d p' p) g = 0 → CategoryTheory.CategoryStruct.comp (K.d p' p) (f - g) = 0