Evtukhov, V. M., and A. M. Klopot. 2013. “Asymptotic Representations for Some Classes of Solutions of Ordinary Differential Equations of Order $n$ With Regularly Varying Nonlinearities”. Ukrains’kyi Matematychnyi Zhurnal 65 (3), 354-80. https://umj.imath.kiev.ua/index.php/umj/article/view/2424.