BarannykT. A., BarannykA. F., and YurykI. I. “Generalized Procedure of Separation of Variables and Reduction of Nonlinear Wave Equations”. Ukrains’kyi Matematychnyi Zhurnal 61, no. 7 (July 25, 2009): 892-905. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3065.