1. Brouwer, D. and Clemence, G. M.: 1961, Methods of Celestial Mechanics, Academic Press, New York and London.
2. Gousidou-Koutita, M.: 1980, Ph.D. Thesis, Manchester University.
3. Hadjidemetriou, J. D.: 1975, Celes. Mech. 12 155.
4. Hadjidemetriou, J. D. 1977, Lectures on Periodic Orbits and their Stability, Université de Paris, VI.
5. Kopal, Z. and Lyttleton, R. A.: 1963, Icarus I, 455.