∀ {T : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} T] {D : Type u_4}
  [inst_1 : CategoryTheory.Category.{u_3, u_4} D] {X : T} {F : CategoryTheory.Functor T D}
  {G : CategoryTheory.Functor D T} (a : F ⊣ G) ⦃X_1 Y : CategoryTheory.Under ((CategoryTheory.Functor.id T).obj X)⦄
  (f : X_1 ⟶ Y),
  CategoryTheory.CategoryStruct.comp
      ((CategoryTheory.Functor.id (CategoryTheory.Under ((CategoryTheory.Functor.id T).obj X))).map f)
      (CategoryTheory.Under.homMk (a.unit.app Y.right) ⋯) =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.Under.homMk (a.unit.app X_1.right) ⋯)
      (((CategoryTheory.Under.post F).comp
            ((CategoryTheory.Under.post G).comp (CategoryTheory.Under.map (a.unit.app X)))).map
        f)