BerezovskyA. A., KonetI. M., LenyukM. P., SamoilenkoA. M., and TeplinskyYu. V. “Ukrainian School-Seminar "Nonlinear Boundary Value Problems of Mathematical Physics and applications"”. Ukrains’kyi Matematychnyi Zhurnal 49, no. 4 (April 25, 1997): 613–617. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5041.