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2. W. Heisenberg,The Physical Principles of the Quantum Theory (University of Chicago Press, Chicago, 1930).
3. M. Born,Natural Philosophy of Cause and Chance (Oxford University Press, London, 1949).
4. P. A. M. Dirac,The Principles of Quantum Mechanics (Clarendon Press, Oxford, 1930).
5. G. Ludwig,Phys. Bl�tter 11, 489 (1955).