DzhumabaevD. S., and TemeshevaS. M. 2018. “Criteria for the Existence of an Isolated solution of a Nonlinear Boundary-Value Problem”. Ukrains’kyi Matematychnyi Zhurnal 70 (3), 356-65. http://umj.imath.kiev.ua/index.php/umj/article/view/1561.