∀ {C : Type u₁} {D : Type u₂} [inst : CategoryTheory.Category.{v₁, u₁} C] [inst_1 : CategoryTheory.Category.{v₂, u₂} D]
  {i : CategoryTheory.Functor D C} [inst_2 : CategoryTheory.Reflective i] (X : i.EssImageSubcategory),
  CategoryTheory.IsIso ((CategoryTheory.reflectorAdjunction i).unit.app X.obj)