BaskakovA. G. “On the Reducibility of Linear Differential Operators With Unbounded Operator Coefficients”. Ukrains’kyi Matematychnyi Zhurnal 45, no. 5 (May 25, 1993): 587–595. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5847.