Dmytryshyn, Yu. B. “Problem Without Initial Conditions for Linear and Almost Linear Degenerate Operator Differential Equations”. Ukrains’kyi Matematychnyi Zhurnal 61, no. 3 (March 25, 2009): 322-332. Accessed April 16, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3022.