1. S.M. Rytov: Trudy FIAN 2(1), 3 (1940).
2. S.M. Rytov: Dokl. Akad. Nauk SSSR 18(2), 263 (1938).
3. R.P. Feynman, A.R. Hibbs: Quantum Mechanics and Path Integrals (McGraw-Hill, New York 1965).
4. V.S. Buslaev: In Problemy Mathematicheskoi Fiziki (problems of mathematical physics), Vol.2 (Izd. LGU, Leningrad 1967) p.85.
5. M.V. Berry, K.E. Mount: Rep. Prog. Phys. 35(4), 315 (1972).