1. Tikhonov, A.N. and Samarskii, A.A., Uravneniya matematicheskoi fiziki (Equations of Mathematical Physics), Moscow: Nauka, 1972.
2. Kapustin, N.Yu. and Moiseev, E.I., Differents. Uravn., 2000, vol. 36, no.10, pp. 1357–1360.
3. Moiseev, E.I. and Kapustin, N.Yu., Dokl. RAN, 2002, vol. 386, no.1, pp. 24–30.