∀ {C : Type u_1} [inst : CategoryTheory.Category.{v, u_1} 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.mappingConeHomOfDegreewiseSplitIso S σ).inv
      (CochainComplex.mappingCone.triangle (CochainComplex.homOfDegreewiseSplit S σ)).mor₃ =
    -(CategoryTheory.shiftFunctor (CochainComplex C ℤ) 1).map S.g