1. Brouwer, D.: 1928, Ann. Sterrew. Leiden 16(1).
2. Brouwer, D. and Clemence, G.M.: 1961, Methods of Celestial Mechanics, Academic Press, New York.
3. de Sitter, w.: 1931, Monthly Notices Roy. Astron. Soc. 91, 706.
4. Emihhizer, C.R., Helleman, R.H.G., and Montroll, E.W.: 1976, J. Math. Phys. 17, 121.
5. Ferraz-Mello, S.: 1966, Bull. Astron. (3e série), 1, 287.