The Cartan - Monge geometric approach to the characteristic method for nonlinear partial differential equations of the first and higher orders. Neliniini Kolyvannya, [S. l.], v. 10, n. 1, p. 26–36, 2007. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/418. Acesso em: 21 jan. 2026.