1. B. Müller, J.Rafelski, W. Greiner, Z.Physik 257, (1972a) 62.
2. B. Müller, J. Rafelski, and W. Greiner, Z. Physik 257 (1972b) 183.
3. P.A.M. Dirac, Proc. Roy. Soc. A 117 (1928) 610.
4. P.A.M. Dirac, Proc. Roy. Soc. A 126 (1930) 360.
5. J.D. Bjorken, and S.D. Drell, Relativistic Quantum Mechanics (1964) and Relativistic Quantum Fields ( 1965 ) ( New York: McGraw Hill ).