1. B. M. Levitan, and I. S. Sargsyan, Sturm-Liouville and Dirac Operators [in Russian], Nauka, Moscow (1988).
2. V. A. Marchenko, Sturm-Liouville Operators and Their Applications [in Russian], Naukova Dumka, Kiev (1977).
3. Yu. M. Berezanskii, “Uniqueness theorem in the inverse spectral problem for the Schrodinger equation,” Tr. Mosk. Mat. Obshch., 7, 3–51 (1958).
4. L. P. Nizhnik, Inverse Scattering Problems for Hyperbolic Equations [in Russian], Naukova Dumka, Kiev (1977).
5. M. G. Gasymov, “Inverse problem of the scattering theory for Dirac systems of order 2n,” Tr. Mosk. Mat. Obshch., 19, 41–112 (1968).