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2. R. P. Feynman, Rev. Mod. Phys. 20, 367 (1948);
3. R. P. Feynman, A. R. Hibbs, Quantum Mechanics and Path Integrals (McGraw-Hill, New York,1965).
4. R. P. Feynman, A. R. Hibbs, D. F. Styer, Quantum Mechanics and Path Integrals (Dover Publications, Mineola, NY, 2010).
5. V. Popov, Functional Integrals in Quantum Field Theory and Statistical Physics (Springer, 1983).