Evtukhov, V. M., and O. R. Shlepakov. 2012. “Asymptotic Representations of Solutions of Essentially Nonlinear Systems of Ordinary Differential Equations With Regularly and Rapidly Varying Nonlinearities”. Ukrains’kyi Matematychnyi Zhurnal 64 (9), 1165-85. https://umj.imath.kiev.ua/index.php/umj/article/view/2650.