1. N. Bourbaki, Groupes et Algèbres de Lie, Ch.VI, Hermann, Paris, 1975.
2. D. H. Collingwood, Representations of rank one Lie groups, Pitman, Boston, 1985.
3. J. Dixmier, Enveloping algebras, North Holland, Amsterdam, 1977.
4. E. Dynkin, Semisimple subalgebras of semisimple Lie algebras, Mat. Sbornik (N.S.) 30 (72) (1952), 349-462 (Russian)
5. English: Amer. Math. Soc. Transl. 6 (1957), 111-244.