1. J. von Neumann, Mathematische Grundlagen der Quantenmechanik, Verlag von Julius Springer, Berlin (1932).
2. H. Weyl, Gruppentheorie und Quantenmechanik, Hirzel-Verlag, Leipzig (1928).
3. E. P. Wigner, “On the quantum correction for thermodynamic equilibrium,” Phys. Rev., 40, 749–759 (1932).
4. K. Husimi, “Some formal properties of the density matrix,” Proc. Phys. Math. Soc. Japan, 22, 264–314 (1940).
5. H. J. Groenewold, “On the principles of elementary quantum mechanics,” Physica, 12, 405–460 (1946).