L. M. Gershtein, “On the solvability of a complete second-order differential equation in Banach space”, Ukr. Mat. Zhurn., vol. 45, no. 10, pp. 1449–1454, Oct. 1993, Accessed: Apr. 09, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/5950