EvtukhovV. M., and Kas’yanovaV. A. 2005. “Asymptotic Behavior of Unbounded Solutions of Essentially Nonlinear Second-Order Differential Equations. I”. Ukrains’kyi Matematychnyi Zhurnal 57 (3), 338–355. https://umj.imath.kiev.ua/index.php/umj/article/view/3602.