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2. G.L. Pollack: Rev. Mod. Phys. 41, 48 (1969)
3. W. Heisenberg: Z. Phys. 43, 172 (1927)
4. N. Bohr: ?The quantum postulate and the recent development of atomic theory?, reprinted in: N. Bohr, Atomic Theory and the Description of Nature (Cambridge University Press, Cambridge 1934)
5. J. von Neumann: Mathematical Foundations of Quantum Mechanics (Princeton University Press, Princeton 1955) originally published in German in 1932