EvtukhovV. M., and Kas’yanovaV. A. 2006. “Asymptotic Behavior of Unbounded Solutions of Essentially Nonlinear Second-Order Differential Equations. II”. Ukrains’kyi Matematychnyi Zhurnal 58 (7), 901–921. https://umj.imath.kiev.ua/index.php/umj/article/view/3505.