I. I. Yuryk, “Nonlinear d’alembert equation in the pseudo-euclidean space $R_{2,n}$ and its solutions”, Ukr. Mat. Zhurn., vol. 52, no. 6, pp. 820–827, Jun. 2000, Accessed: Apr. 23, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/4476