{C : Type u} →
  [inst : CategoryTheory.Category.{v, u} C] →
    [inst_1 : CategoryTheory.Abelian C] →
      [inst_2 : CategoryTheory.HasExt C] →
        {X Y : C} →
          [inst_3 : HasDerivedCategory C] →
            {a : ℕ} →
              CategoryTheory.Abelian.Ext X Y a →
                CategoryTheory.ShiftedHom ((DerivedCategory.singleFunctor C 0).obj X)
                  ((DerivedCategory.singleFunctor C 0).obj Y) ↑a