1. Arnold, V. I.: 1963,Uspekhi Mat. Nauk 18, 91, Translation by: Foreign Technology Division, Air Force Systems Command.
2. Contopoulos, G.: 1960,Z. Astrophys. 49, 273.
3. Contopoulos, G.: 1966,Ap. J. Suppl. No. 122,13.
4. Contopoulos, G.: 1967,Bull. Astron. 2, 223.
5. Contopoulos, G.: 1968,Ap. J. (in press).