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, Vol. 70, no. 1, Jan. 2018, pp. 94-114, http://umj.imath.kiev.ua/index.php/umj/article/view/1544.