1. B. d’Espagnat:Conceptual Foundations of Quantum Mechanics (Menlo Park, Cal., 1971).
2. B. d’Espagnat: inPreludes in Theoretical Physics, edited byA. De-Shalit, H. Feshbach andL. Van Hove (Amsterdam, 1966), p. 185.
3. J. von Neumann:Mathematical Foundations of Quantum Mechanics (Princeton, N. J., 1955), p. 429.
4. D. Bohm:Quantum Theory (Englewood Cliff, N. J., 1951).
5. W. H. Furry: inLectures in Theoretical Physics, Vol.8 A, edited byW. E. Brittin (Boulder, Colo., 1966), p. 41.