∀ {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] (F : CategoryTheory.Functor D T) {X : T} (Y : CategoryTheory.Over X)
  (x : CategoryTheory.CostructuredArrow (CategoryTheory.CostructuredArrow.toOver F X) Y),
  CategoryTheory.CategoryStruct.comp
      (F.map
        (CategoryTheory.Iso.refl
            ((CategoryTheory.Functor.id
                      (CategoryTheory.CostructuredArrow (CategoryTheory.CostructuredArrow.toOver F X) Y)).obj
                  x).left.left).hom)
      (((CategoryTheory.CostructuredArrow.costructuredArrowToOverEquivalence.functor F Y).comp
                (CategoryTheory.CostructuredArrow.costructuredArrowToOverEquivalence.inverse F Y)).obj
            x).left.hom =
    ((CategoryTheory.Functor.id (CategoryTheory.CostructuredArrow (CategoryTheory.CostructuredArrow.toOver F X) Y)).obj
          x).left.hom