EGORCHENKO, I. A.; POPOVICH, R. O. Group Classification of Generalized Eikonal Equations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 53, n. 11, p. 1513–1520, 2001. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4371. Acesso em: 6 dec. 2025.