1. A. G. Sveshnikov, A. B. Al’shin, M. O. Korpusov, and Yu. D. Pletner, Linear and Nonlinear Equations of Sobolev Type (Fizmatlit, Moscow, 2006) [in Russian].
2. V. L. Bonch-Bruevich and S. G. Kalashnikov, Physics of Semiconductors (Nauka, Moscow, 1990) [in Russian].
3. V. L. Bonch-Bruevich, I. P. Zvyagin, and A. G. Mironov, Domain Electrical Instabilities in Semiconductors (Nauka, Moscow, 1972; Consultants Bureau, New York, 1975).
4. M. M. Vainberg, Variational Methods for Analysis of Nonlinear Operators (Gostekhteorizdat, Moscow, 1956) [in Russian].