∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] {D : Type u_4}
  [inst_1 : CategoryTheory.Category.{u_3, u_4} D] {F : CategoryTheory.Functor C D} {G : CategoryTheory.Functor D C}
  (adj : CategoryTheory.Adjunction.CoreUnitCounit F G) (Y : D),
  CategoryTheory.CategoryStruct.comp (adj.unit.app (G.obj Y)) (G.map (adj.counit.app Y)) =
    CategoryTheory.CategoryStruct.id (G.obj Y)