∀ {T : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} T] {X : T} (f : CategoryTheory.Over X)
  (g : CategoryTheory.Over f),
  CategoryTheory.CategoryStruct.comp
      (CategoryTheory.Iso.refl ((CategoryTheory.Functor.id (CategoryTheory.Over f)).obj g).left.left).hom
      ((f.iteratedSliceForward.comp f.iteratedSliceBackward).obj g).left.hom =
    ((CategoryTheory.Functor.id (CategoryTheory.Over f)).obj g).left.hom