Fushchich VI, Revenko IV, Zhdanov RZ. Separation of variables in two-dimensional wave equations with potential. Ukr. Mat. Zhurn. [Internet]. 1994Oct.25 [cited 2024Jul.27];46(10):1343–1361. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/5613