∀ {T : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} T] (X : T) {Z Y : (CategoryTheory.Under X)ᵒᵖ} (f : Z ⟶ Y),
  CategoryTheory.CategoryStruct.comp f.unop.right.op (CategoryTheory.Over.mk (Opposite.unop Y).hom.op).hom =
    (CategoryTheory.Over.mk (Opposite.unop Z).hom.op).hom