On a Maximum Principle and Uniqueness Theorems for a System of First Order Equations of Mixed Type. Journal of Partial Differential Equations, [S. l.], v. 9, n. 3, p. 251–262, 1996. Disponível em: https://www.global-sci.com/index.php/jpde/article/view/3830. Acesso em: 6 dec. 2025.