1. Vilenkin N. J.,Special Functions and the Theory of Group Representation (American Mathematical Society, Providence) 1968.
2. Araki S.,J. Math. Osaka City Univ.,13 (1962) 1.
3. Lie S.,Differentialgleichungen (Teubner, Leipzig) 1891;Olver P.,Applications of Lie Groups to Differential Equations (Springer, Berlin) 1986.
4. Helgason S.,Differential Geometry and Symmetric Spaces (Academic Press, New York, N.Y.) 1962.
5. Cartan E.,Rend. Circ. Mat. Palermo,53 (1929) 217.