Samoilenko, A. M. (2002). On the Asymptotic Integration of a System of Linear Differential Equations with a Small Parameter in the Coefficients of a Part of Derivatives.
Ukrains’kyi Matematychnyi Zhurnal,
54(11), 1505-1517.
https://umj.imath.kiev.ua/index.php/umj/article/view/4188