$U_m\left(\xi \right)\sim D_m\left(\xi \right)-\frac{1}{2^{6}h}\left(D_{m+4}\left(\xi \right)-4!m4D_{m-4}\left(\xi \right)\right)+\frac{1}{2^{13}{h}^2}\left(D_{m+8}\left(\xi \right)-2^5\left(m+2\right)D_{m+4}\left(\xi \right)+4!2^5\left(m-1\right)m4D_{m-4}\left(\xi \right)+8!\frac{m}{8}{D}_{m-8}\left(\xi \right)\right)+\cdots$