Evtukhov, V. M., and A. V. Droggina. 2019. “Asymptotic Representations of Solutions of Nonautonomous Ordinary Differential Equations”. Ukrains’kyi Matematychnyi Zhurnal 71 (12), 1626-46. https://umj.imath.kiev.ua/index.php/umj/article/view/1006.