∀ {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
      ((CategoryTheory.CostructuredArrow.toOver F X).map
        (CategoryTheory.CostructuredArrow.isoMk
            (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).hom =
    ((CategoryTheory.Functor.id (CategoryTheory.CostructuredArrow (CategoryTheory.CostructuredArrow.toOver F X) Y)).obj
        x).hom