1. Canal, R. and Schatzman, E., 1974a, C.R.Acad. Sci. Paris, 279, B-681.
2. Canal, R. and Schatzman, E., 1974b, Mem. Soc. Astron. Ital., 45, 763
3. Canal, R. and Schatzman, E., 1976, Astron. Astrophys., 46, 229
4. D'Antona, F. and Ergma, E., 1993, Astron. Astrophys., 269, 219
5. Ergma, E., 1993, Astron. Astrophys., 273, L38.