Yehorchenko I. A., and VorobyovaA. I. “Conditional and Hidden Infinite-Dimensional Symmetries of Wave Equations”. Ukrains’kyi Matematychnyi Zhurnal 74, no. 3 (April 26, 2022): 335-341. Accessed December 22, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/7035.