{C : Type u_1} →
  [inst : CategoryTheory.Category.{v, u_1} C] →
    [inst_1 : CategoryTheory.Preadditive C] →
      [inst_2 : CategoryTheory.Limits.HasBinaryBiproducts C] →
        {X₁ X₂ X₃ : CochainComplex C ℤ} →
          (f : X₁ ⟶ X₂) →
            (g : X₂ ⟶ X₃) →
              HomotopyEquiv (CochainComplex.mappingCone g)
                (CochainComplex.mappingCone (CochainComplex.mappingConeCompTriangle f g).mor₁)