∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] [inst_1 : CategoryTheory.Abelian C] {Z : C}
  (I : CategoryTheory.InjectiveResolution Z),
  { X₁ := ((CochainComplex.single₀ C).obj Z).X 0, X₂ := I.cocomplex.X 0, X₃ := I.cocomplex.X 1, f := I.ι.f 0,
      g := I.cocomplex.d 0 1, zero := ⋯ }.Exact