∀ {C : Type u_3} [inst : CategoryTheory.Category.{u_1, u_3} C] {J : CategoryTheory.GrothendieckTopology C}
  {F F' : CategoryTheory.Sheaf J (Type u_2)} (f : F ⟶ F'),
  CategoryTheory.Presheaf.IsSheaf J
    (CategoryTheory.Subfunctor.sheafify J (CategoryTheory.Subfunctor.range f.val)).toFunctor