∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] [inst_1 : CategoryTheory.Abelian C]
  [inst_2 : CategoryTheory.HasExt C] {S : CategoryTheory.ShortComplex C} (hS : S.ShortExact) (Y : C) (n₀ n₁ : ℕ)
  (h : 1 + n₀ = n₁), (CategoryTheory.Abelian.Ext.contravariantSequence hS Y n₀ n₁ h).Exact