1. S. Albeverio, P. Kurasov, Singular perturbations of differential operators, Cambridge Univ. Press, 2000.
2. S. Albeverio, P. Kurasov, Rank one perturbations of not semibounded operators, Integr. equ. oper. theory 27 (1997), 379–400.
3. S. Albeverio, P. Kurasov, Rank one perturbations, approximations, and selfadjoint extensions, J. Func. Anal. 148 (1997), 152–169.
4. D.Z. Arov, Scattering theory with dissipation of energy, English transl. in Dokl. Akad. Nauk SSSR 216 (1974), 713–716.
5. T. Azizov, I. Iokhvidov, Linear operators in spaces with an indefinite metric, Wiley-Interscience Publ., John Wiley & Sons Ltd., Chichester, 1989.