EgorchenkoI. A., and PopovichR. O. “Group Classification of Generalized Eikonal Equations”. Ukrains’kyi Matematychnyi Zhurnal 53, no. 11 (November 25, 2001): 1513-1520. Accessed November 22, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4371.