Evtukhov, V. M. “Asymptotics of Solutions of Nonautonomous Second-Order Ordinary Differential Equations Asymptotically Close to Linear Equations”. Ukrains’kyi Matematychnyi Zhurnal 64, no. 10 (October 25, 2012): 1346–1364. Accessed April 11, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/2663.