S. S. Yusubov, “Goursat-Type Problem for a Higher-Order Equation”, Ukr. Mat. Zhurn., vol. 65, no. 6, pp. 874–880, Jun. 2013, Accessed: Apr. 23, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/2474