Y. P. Apakov, “Third boundary-value problem for a third-order differential equation with multiple characteristics”, Ukr. Mat. Zhurn., vol. 70, no. 9, pp. 1274–1281, Sep. 2018, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/1633