ShklyarA. Ya. “Correctness of the Cauchy Problem for Trinomial Higher-Order Operator Differential Equations”. Ukrains’kyi Matematychnyi Zhurnal 45, no. 5 (May 25, 1993): 704–714. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5857.