1. D. Mihalas, Stellas Atmospheres, Freeman, San Francisco (1970).
2. S. G. Slyusarev, Dokl. Akad. Nauk SSSR,95, 741 (1954).
3. V. V. Sobolev, Dokl. Akad. Nauk SSSR,111, 1000 (1956).
4. V. V. Sobolev, Dokl. Akad. Nauk SSSR,212, 1095 (1973).
5. R. E. Bellman and R. E. Kalaba, Proc. Nat. Acad. Sci. USA,42, 629 (1956).