{C : Type u₁} →
  [inst : CategoryTheory.Category.{v₁, u₁} C] →
    {D : Type u₂} →
      [inst_1 : CategoryTheory.Category.{v₂, u₂} D] →
        {L : CategoryTheory.Functor C D} →
          {R : CategoryTheory.Functor D C} → (L ⊣ R) → (L.comp R ≅ CategoryTheory.Functor.id C) → L.FullyFaithful