BugirM. K. “Conditions of Nonoscillation of Binomial Systems of Differential Equations”. Ukrains’kyi Matematychnyi Zhurnal 49, no. 6 (June 25, 1997): 836–841. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5069.