1. Seee.g. J. M. Jauch:Foundations of Quantum Mechanics (Reading, Mass., 1968);J. M. Levy-Leblond:Riv. Nuovo Cimento,4, 99 (1974).
2. E. Inonu andE. P. Wigner:Nuovo Cimento,9, 705 (1952);V. Bargmann:Ann. Math.,59, 1 (1954);M. Hamermesh:Ann. of Phys.,9, 518 (1960).
3. J. M. Jauch:Helv. Phys. Acta,37, 284 (1964);J. M. Jauch:Foundations of Quantum Mechanics (Reading, Mass., 1968);E. Celeghini, L. Lusanna andE. Sorace:Nuovo Cimento,31 A, 89 (1976);P. Roman andJ. P. Leveille:Journ. Math. Phys.,15, 1760 (1974);H. Hoogland:J. Phys. A,11, 797 (1978); For a clear discussion of the whole problem see:J. M. Levy-Leblond:Riv. Nuovo Cimento,4, 99 (1974).
4. E. P. Wigner:Physics Today (March 1964), p. 34.
5. See,e.g.:L. D. Landau andE. M. Lifshitz:Quantum Mechanics (Non relativistic Theory) (London, 1958).