Boichuk О. A. and L. M. Shehda, “Degenerate nonlinear boundary-value problems”, Ukr. Mat. Zhurn., vol. 61, no. 9, pp. 1174–1188, Sep. 2009, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3090