V. I. Fushchich, I. V. Revenko, and R. Z. Zhdanov, “Separation of variables in two-dimensional wave equations with potential”, Ukr. Mat. Zhurn., vol. 46, no. 10, pp. 1343–1361, Oct. 1994, Accessed: Feb. 17, 2026. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/5613