Il’kiv, V. S. “A Problem With Formal Initial Conditions for Differential Equations With Constant Pseudodifferential Coefficients”. Ukrains’kyi Matematychnyi Zhurnal 50, no. 7 (July 25, 1998): 877–888. Accessed May 19, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4868.