1. I. M. Gel’fand and B. M. Levitan, “On the determination of a differential equation by its spectral function,” Izv. Akad. Nauk SSSR, Ser. Mat., 15, No. 4, 309–360 (1951).
2. V. E. Zakharov and A. B. Shabat, “Exact theory of two-dimensional self-focusing and one-dimensional self-modulation of wave in nonlinear media,” Zh. _ksp. Teor. Fiz., 61, No. 1, 118–134 (1971); English translation: J. Exp. Theor. Phys., 34, No. 1, 62–69 (1972).
3. M. A. Lavrent’ev and B. V. Shabat, Methods of the Theory of Functions of Complex Variable [in Russian], Nauka, Moscow (1973).
4. V. A. Marchenko, Sturm–Liouville Operators and Their Applications [in Russian], Naukova Dumka, Kiev (1977).
5. Z. T. Nazarchuk and A. T. Synyavs’kyi, “Approximation of the solution of inverse problem of scattering of electromagnetic waves on plane dielectrics,” Fiz.-Khim. Mekh. Mater., 47, No. 1, 7–17 (2011); English translation: Mater. Sci., 47, No. 1, 1–13 (2011).