∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] [inst_1 : CategoryTheory.Abelian C]
  [inst_2 : CategoryTheory.HasExt C] (X : C) {Y : C} (R : CategoryTheory.InjectiveResolution Y) (n : ℕ),
  R.extEquivCohomologyClass 0 = 0