∀ {C : Type u₁} {D : Type u₂} [inst : CategoryTheory.Category.{v₁, u₁} C] [inst_1 : CategoryTheory.Category.{v₂, u₂} D]
  {F : CategoryTheory.Functor C D} {X : D},
  F.isDenseAt X ↔
    Nonempty
      (CategoryTheory.Limits.IsColimit
        ((CategoryTheory.Functor.LeftExtension.mk (CategoryTheory.Functor.id D) F.rightUnitor.inv).coconeAt X))