\[\int_{0}^{\pi/2}R_{F}\left({\sin}^{2}\theta{\cos}^{2}\left(x+y\right),{\sin}^{%
2}\theta{\cos}^{2}\left(x-y\right),1\right)\,\mathrm{d}\theta=R_{F}\left(0,{%
\cos}^{2}x,1\right)R_{F}\left(0,{\cos}^{2}y,1\right),\]