1. H. Yilmaz,Introduction to the Theory of Relativity and the Principles of Modern Physics (Blaisdell Publ. Co., Ginn and Company, New York, 1965), pp. 73, 74.
2. W. Pauli,Theory of Relativity (Pergamon Press, New York, 1958), pp. 224, 225.
3. G. Holton,Am. J. Phys. 28, 627 (1960), p. 632.
4. J. A. Wheeler,Geometrodynamics (Academic Press, New York, 1962).
5. P. A. M. Dirac,Sci. Am. 208(5), 49 (1963).