1. E. Wigner:Ann. Math.,40, 149 (1939).
2. V. Bargmann:Ann. Math.,48, 568 (1947).
3. Yu. M. Shirokov:Sov. Phys. JETP,6 (33), 919 (1958);6 (33), 929 (1958);M. A. Naimark:Les représentations linéaires du groupe de Lorentz (Paris, 1962);N. Gel’fand, R. A. Minlos andYa. Shapiro:Representations of the Rotation and the Lorentz Groups and Their Applications (Oxford, 1963). For more recent work and references cf.,L. C. Biedenharn, J. Nuyts andN. Straumann: CERN preprint 65/761/5-TH. 555 (1965);A. O. Barut andC. Fronsdal: IC/65/22 (Trieste);E. M. Stein: (Lecture)Seminar on Theor Phys. (Trieste, 1965), p. 563.
4. E. Wigner: (Lecture) Seminar on Theory. Phys. (Trieste, 1962), p. 64.
5. E. Wigner:Group Theory (New York, 1959). Original papers:E. Wigner:Zeits. Phys.,43, 624 (1927);