1. Marchenko, V.A.: Sturm-Liouville Operators and Their Applications. Naukova Dumka, Kiev (1977) (Russian)
2. English transl., Birkhauser (1986)
3. Levitan, B.M.: Inverse Sturm-Liouville Problems. Nauka, Moscow (1984) (Russian)
4. English transl., VNU Sci. Press, Utrecht (1987)
5. Pöschel, J., Trubowitz, E.: Inverse Spectral Theory. Academic Press, New York (1987)