1. Hohl, F, 1977, NASA TR R-343.
2. Hohl, F. 1975, in IAU Symposium No. 69, “Dynamics of Stellar Systems, ed, A. Hayli (Dordrecht, Neth: Reidei), pp. 349.
3. Kalnajs, A.J. 1972, Ap. J. 175, pp. 63.
4. Ostriker, J.P and Peebles, P.J.E. 1973, Ap.J. 186, pp. 467.
5. Rogstad, D.H. and Shostak, G.S. 1972, Ap. J. 176, pp. 315.