1. L. I. Schiff:Quantum Mechanics (New York, 1949). A particular case of the Theorem I referring to a one-dimensional minimum wave packet is considered on pp. 54–59.
2. J. M. Jauch:Helv. Phys. Acta (in print).
3. J. M. Jauch:Helv. Phys. Acta,31, 127 (1958).
4. An outline of the mathematical theory will be found in reference (3). More detailed expositions will be found inB. von Sz.-Nagy:Ergebnisse der Mathematik und Ihrer Grenzgebiete,5, 5 (1942);F. Riesz andB. von Sz.-Nagy:Functional Analysis (New York, 1955).
5. J. von Neumann:Math. Ann.,104, 570 (1931). It may not be superfluous to point out here that the terms wave packet and element of a Hilbert space are synonymous.