∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] [inst_1 : CategoryTheory.Abelian C]
  [inst_2 : HasDerivedCategory C] {S : CategoryTheory.ShortComplex (CochainComplex C ℤ)} (hS : S.ShortExact),
  (DerivedCategory.triangleOfSES hS).obj₂ = DerivedCategory.Q.obj S.X₂