1. L. Pauling and E. B. Wilson, An Introduction to Quantum Mechanics, McGraw-Hill, 1935, p. 422.
2. Dirac, Quantum Mechanics, Oxford, 1930, §4.
3. For the existence of mathematical causation, cf. also p. 65 of Heisenberg’s Dirac The Physical Principles of the Quantum Theory, Chicago, 1929.
4. Cf. J. von Neumann, Mathematische Grundlagen der Quanten-mechanik, Berlin, 1931, p. 18.
5. Cf. J. von Neumann, ‘Operatorenmethoden in der klassischen Mechanik,’ Annals of Math.
33 (1932), 595–8. The difference of two sets S
1
, S
2 is the set (S
1+S
2) — S
1·S
2 of those points, which belong to one of them, but not to both.