1. Arnold, V. & Avez, A.: 1989, Ergodic Problems of Classical Mechanics, (New York: Addison-Wesley), 2nd. ed.
2. Cincotta, P. & Simó, C.: 1998, preprint
3. Contopoulos, G. & Voglis, N.: 1996, Cel. Mech. & Dynam. Astron., 64, 1
4. Fraser, A. & Swinney, H.: 1986, Phys. Rev. A, 33, 1134
5. Hénon, M. & Heiles, C.: 1964, AJ, 69, 73