1. Contopoulos, G. and Zikides, M.: 1980,Astron. Astrophys. 90, 198.
2. Heggie, D. C.: 1983,Celest. Mech. 29, 207.
3. Plemelj, J.: 1962,Problems in the Sense of Riemann and Klein, Interscience Publishers, New York.
4. Poincaré, H.: 1892,Les méthodes nouvelles de la mécanique céleste, Vol. 1.
5. Whittaker, E. T.: 1936,A Treatise on the Analytical Dynamics of Particles and Rigid Bodies, Cambridge University Press, New York.