V. P. Yakovets, “Construction of Asymptotic Solutions of Linear Systems of Differential Equations with Two Small Parameters”, Ukr. Mat. Zhurn., vol. 55, no. 7, pp. 961–976, Jul. 2003, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3971