1. W. Heitler, The Quantum Theory of Radiation, Second ed. S. 17, 64. Oxford-Univ. Press, London, 1949.
2. J. M. Jauch undK. M. Watson, Phys. Rev.74, 950, 1948.
3. K. F. Novobátzky, Hung. Acta Phys.1, No. 5. 1959.
4. M. v. Laue, Die Relativitätstheorie, Bd.I, S. 107, Vieweg, Braunschweig, 1953.
5. G. Ludwig, ZS. f. Phys.130, 468, 1951.