∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.Preadditive C]
  (S : CategoryTheory.ShortComplex (CochainComplex C ℤ))
  (σ : (n : ℤ) → (S.map (HomologicalComplex.eval C (ComplexShape.up ℤ) n)).Splitting)
  [inst_2 : CategoryTheory.Limits.HasBinaryBiproducts C],
  CategoryTheory.CategoryStruct.comp (CochainComplex.triangleOfDegreewiseSplit S σ).rotate.rotate.mor₁
      (CategoryTheory.Iso.refl (CochainComplex.triangleOfDegreewiseSplit S σ).rotate.rotate.obj₂).hom =
    CategoryTheory.CategoryStruct.comp
      (CategoryTheory.Iso.refl (CochainComplex.triangleOfDegreewiseSplit S σ).rotate.rotate.obj₁).hom
      (CochainComplex.mappingCone.triangle (CochainComplex.homOfDegreewiseSplit S σ)).mor₁