Evtukhov, V. M., & Samoilenko, A. M. (2010). Conditions for the existence of solutions of real nonautonomous systems of quasilinear differential equations vanishing at a singular point. Ukrains’kyi Matematychnyi Zhurnal, 62(1), 52 - 80. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/2843