\[(z_{\pm}^{2}-z_{\mp}^{2})R_{D}\left(x^{2},y^{2},z^{2}\right)={2(z_{\pm}^{2}-a^%
{2})}R_{D}\left(a^{2},z_{\mp}^{2},z_{\pm}^{2}\right)-3R_{F}\left(x^{2},y^{2},z%
^{2}\right)+(3/z),\]