YakovetsV. P. “On the Structure of the General Solution of a Degenerate Linear System of Second-Order Differential Equations”. Ukrains’kyi Matematychnyi Zhurnal 50, no. 2 (February 25, 1998): 292–298. Accessed October 6, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4962.