1. S. Krylov, V.A. Fock, Zh. Eksp. Teor. Fiz. 17, 93 (1947)
2. A.N. Kolgomorov, S.V. Fomin, Elements of the Theory of Functions and Functional Analysis (Dover Publ. Inc., 1999)
3. L.A. Khalfin, Zh. Eksp. Teor. Fiz. 33, 1371 (1957), Sov. Phys. JETP 6, 1053 (1958)
4. R.E.A.C. Paley, N. Wiener, Fourier transforms in the complex domain (American Mathematical Society, New York, 1934)
5. L. Fonda, G.C. Ghirardii, A. Rimini, Rep. Prog. Phys. 41, 587 (1978)