Shigeyasu Kamiya "Notes on some classical series associated with discrete subgroups of $U\left( {1,n;C} \right)$ on $\partial B^n \times \partial B^n \times \partial B^n $," Proceedings of the Japan Academy, Series A, Mathematical Sciences, Proc. Japan Acad. Ser. A Math. Sci. 68(6), 137-139, (1992)