V. S. Il'kiv, “A problem with formal initial conditions for differential equations with constant pseudodifferential coefficients”, Ukr. Mat. Zhurn., vol. 50, no. 7, pp. 877–888, Jul. 1998, Accessed: Apr. 13, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/4868