EvtukhovV. M., and SamoilenkoA. M. “Conditions for the Existence of Solutions of Real Nonautonomous Systems of Quasilinear Differential Equations Vanishing at a Singular Point”. Ukrains’kyi Matematychnyi Zhurnal 62, no. 1 (January 25, 2010): 52 - 80. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2843.