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2. Taub, A. H., Ann. Math., 53, 472 (1951).
3. McVittie, G. C., J. Rational Mech. and Analysis, 4, 201 (1955).
4. Scheidegger, A. E., Rev. Mod. Phys., 25, 451 (1953). See also Brdička, M., Proc. Roy. Irish Acad., 54, 137 (1951).
5. Bondi, H., various contributions to discussions at the International Conference on Gravitation, Chapel Hill, N.C., 1957.