1. G. Ludwig:Lecture Notes in Physics, Vol.4 (Berlin, 1970).
2. G. Ludwig: inFoundations of Quantum Mechanics, edited byB. D’Espagnat (New York, N.Y., 1971), p. 287.
3. G. Ludwig:Mess-und Präparierprozesse, inNotes in Math. Phys., Vol.6 (Marburg, 1972).
4. G. Ludwig: inThe Physicist’s Conception of Nature, edited byJ. Mehra (Dordrecht, 1973), p. 702.
5. G. Ludwig: inThe Uncertainty Principle and Foundations of Quantum Mechanics, edited byW. C. Price andS. S. Chissick (New York, N.Y., 1977), p. 189.