BerezovskyA. A.; KonetI. M.; LenyukM. P.; SamoilenkoA. M.; TeplinskyY. V. Ukrainian school-seminar "Nonlinear boundary value problems of mathematical physics and applications". Ukrains’kyi Matematychnyi Zhurnal, v. 49, n. 4, p. 613–617, 25 Apr. 1997.