PuzaB., RontoA. M., RontoM. I., and ShchobakN. “On Solutions of Nonlinear Boundary-Value Problems the components of Which Vanish at Certain Points”. Ukrains’kyi Matematychnyi Zhurnal 70, no. 1 (January 25, 2018): 94-114. Accessed November 27, 2020. http://umj.imath.kiev.ua/index.php/umj/article/view/1544.