1. Heckmann, O., and Schücking, E. (1962). ?Relativistic Cosmology,? inGravitation, ed. Witten, L. (Wiley, New York).
2. MacCallum, M. A. H. (1973). inCargese Lectures in Physics, ed. Schatzman, E. (Gordon & Breach, New York). General studies on spatially homogeneous models have been performed by many authors, see e.g. [24] belowCommun. Math. Phys.,12, 108; Ellis, G. F. R., and MacCallum, M. A. H. (1970).Commun. Math. Phys.,19, 31; King, A. R., and Ellis, G. F. R. (1973).Commun. Math. Phys.,31, 209; Ozsvath, I. (1970).J. Math. Phys.,11, 2860.
3. Ryan, M. P., and Shepley, L. C. (1975).Homogeneous Relativistic Cosmologies, (Princeton Series in Physics, Princeton, New Jersey,); a comprehensive guide to the literature in spatially homogeneous models will be found in this book.
4. Yano, K. (1951).J. Ind. Math. Soc.,15, 105.
5. Katzin, G. H. Levine, J., and Davis, W. R. (1968).J. Math. Phys.,9, 497.