1. Wigner, E. P.: Ann. Math. 40, 149 (1939).
2. Bargmann, E. P., Wigner, E. P.: Proc. Nat. Acad. Sci. (USA) 34, 211 (1948).
3. Heisenberg, W.: Nucl. Phys. 4, 532 (1957).
4. Heisenberg, W.: Introduction to the Unified Field Theory of Elementary Particles, Wiley, London 1967.
5. Fonda, L., Ghirardi, G. I.: Symmetry Principles in Quantum Physics, M. Dekker Inc., New York 1970.