Y. B. Dmytryshyn, “Problem without initial conditions for linear and almost linear degenerate operator differential equations”, Ukr. Mat. Zhurn., vol. 61, no. 3, pp. 322–332, Mar. 2009, Accessed: Feb. 17, 2026. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3022