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2. 1. Galactic Structure (Ithaca, 1965), Volume IX of Lectures in Applied Mathematics
3. edited by Jürgen Ehlers (American Mathematical Society, Providence, R.I., 1967).
4. Brandeis University 1968 Summer Institute in Theoretical Physics: Astrophysics and General Relativity, Volume 2; edited by M. Chrétien, S. Deser, and J. Goldstein (Gordon and Breach); pp. 239-329.
5. Proceedings of IAU Symposium No. 38, Basel, Switzerland, August 29-September 4, 1969; edited by W. Becker and G. Contopoulos (Reidel, The Netherlands).