1. Birkhoff, G.: 1960,Hydrodynamics, Princeton University Press, Princeton, N.J., Chapter 5.
2. Bozis, G.: 1983,Celes. Mech. 31, 129.
3. Broucke, R. and Lass, H.: 1977,Celes. Mech. 16, 215.
4. Courant, R. and Hilbert, D.: 1966,Methods of Mathematical Physics, Vol. II:Partial Differential Equations, Interscience Publishers, New York.
5. Gonzalez-Gascon, F., Gonzalez-Lopez, A., and Pascual-Broncano, P.: 1984,Celes. Mech. 33, 85.