1. S. Helgason, Differential Geometry, Lie Groups, and Symmetric Spaces, Am. Math. Soc., Providence, R.I., 2001.
2. I. M. Gel’fand, “The Center of an Infinitesimal Group Ring”, Mat. Sb. (N.S.), 26(68):1 (1950), 103–112.
3. I. M. Gel’fand, “Spherical Functions on Symmetric Riemannian Spaces”, Dokl. Akad. Nauk SSSR, 70:1 (1950), 5–8.
4. M. A. Olshanetsky and A. M. Perelomov, “Quantum Systems Related to Root Systems, and Radial Parts of Laplace Operators”, Funct. Anal. Appl., 12:2 (1978), 121–128.
5. N. Ya. Vilenkin, Special Functions and the Theory of Group Representations, AMS, Providence, RI, 1968.