∀ {C : Type u_1} [inst : CategoryTheory.Category.{v_1, u_1} C] [inst_1 : CategoryTheory.Preadditive C]
  [inst_2 : CategoryTheory.Limits.HasBinaryBiproducts C] {K₁ L₁ K₂ L₂ : CochainComplex C ℤ} (φ₁ : K₁ ⟶ L₁)
  (φ₂ : K₂ ⟶ L₂) (a : K₁ ⟶ K₂) (b : L₁ ⟶ L₂)
  (comm : CategoryTheory.CategoryStruct.comp φ₁ b = CategoryTheory.CategoryStruct.comp a φ₂),
  (CochainComplex.mappingCone.triangleMap φ₁ φ₂ a b comm).hom₂ = b