1.
Er’omenko VO. Periodic solutions of systems of two linear first-order ordinary differential equations with degenerate asymmetric matrix with derivatives. Ukr. Mat. Zhurn. [Internet]. 1998Mar.25 [cited 2024Nov.24];50(3):350–356. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/4936