1. A.O. Barut and R. Rączka, Theory of Group Representations and Applications, II edition, (Polish Sci. Publ., Warsaw, 1980).
2. A.W. Knapp and E.M. Stein, Ann. Math. 93 (1971) 489; Inv. Math. 60 (1980) 9.
3. B. Kostant, Lecture Notes in Math., Vol.466 (Springer-Verlag, Berlin, 1975) p. 101.
4. D.P. Zhelobenko, Math. USSR Izv. 10 (1976) 1003.
5. V.K. Dobrev, Rep. Math. Phys. 25 (1988) 159.