DzhumabaevD. S., and UteshovaR. E. 2017. “Weighted Limit Solution of a Nonlinear Differential equation at a Singular Point and Its Property”. Ukrains’kyi Matematychnyi Zhurnal 69 (12), 1717-22. https://umj.imath.kiev.ua/index.php/umj/article/view/1815.