1. Bozis, G. and Christides, Th.: 1976,Celes. Mech. 12, 277.
2. Bozis, G. and Hadjidemetriou, J. D.: 1976,Celes. Mech., to appear.
3. Broucke, R. A. and Boggs, D.: 1975,Celes. Mech. 11, 13.
4. Broucke, R. A.: 1976,Celes. Mech., to appear.
5. Delibaltas, P.: 1976, in preparation.