BerezovskyA. A., LenyukM. P., & SamoilenkoA. M. (1996). School-Seminar “Nonlinear boundary-value problems in Mathematical Physics and their applications”. Ukrains’kyi Matematychnyi Zhurnal, 48(6), 863-865. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/5289