1. P. A. M. Dirac, The Principle of Quantum Mechanis, 4th ed., Pergamon, Oxford (1958).
2. E. Schrödinger, Ann. Phys. (Leipzig), 79, 489 (1926).
3. L. D. Landau, Z. Phys., 45, 430 (1927).
4. J. von Neumann, Mathematische Grundlagen der Quantummechanyk, Springer, Berlin (1932).
5. N. N. Bogolyubov and D. V. Shirkov, Introduction to Quantum Field Theory [in Russian], Nauka, Moscow (1976).