1. Arik, M., and Coon, D. D. (1976).Journal of Mathematical Physics,17, 524.
2. Born, M., and Jordan, P. (1925).Zeitschrift f�r Physik, [reprinted inSources of Quantum Mechanics (B. L. van der Waerden, ed.), Dover, New York (1968)].
3. Brodimas, G., Jannussis, A., Sourlas, D., Zisis, V., and Poulopoulos, P. (1981).Lettere al Nuovo Cimento,31, 177.
4. Franke, W., and K�lnay, A. J. (1970).Journal of Mathematical Physics,11, 1729.
5. Garbaczewski, P. (1985). Talk at the International Conference on Quantum Statistics and Foundational Problems of Quantum Mechanics, Jan 28?Feb 1, Calcutta.