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2. Fowler, W. A., Rev. Mod. Phys., 36, 545 (1964). Zel'dovich, I. B., and Novikov, I. D., Russian Physics Quarterly, 2, 52 (1965).
3. Oppenheimer, J. R., and Snyder, H., Phys. Rev., 56, 455 (1939).
4. Compare with Gödel, K., in Albert Einstein, Philosopher-Scientist, edit. by Schilpp, P. A., 555 (Harper and Brothers Publishers, New York, 1951). See also comments by Einstein, Albert Einstein, Philosopher-Scientist, 687.
5. Chandrasekhar, S., Astrophys. J., 140, 417 (1964).