1. J. von Neumann,Mathematical Foundations of Quantum Mechanics (Princeton Univ. Press, 1955), Chapter IV, ��1, 2.
2. A. M. Gleason,J. Math. Mech. 6, 885 (1957).
3. J. M. Jauch and C. Piron,Helv. Phys. Acta 36, 827 (1963).
4. J. M. Jauch,Foundations of Quantum Mechanics (Addison-Wesley, Reading, Mass., 1968), Chapter 7.
5. S. Kochen and E. P. Specker,J. Math. Mech. 17, 59 (1967).