GEORGIEV, S.; MAJDOUB, M. Two nonnegative solutions for two-dimensional nonlinear wave equations. CUBO, A Mathematical Journal, [S. l.], v. 24, n. 3, p. 393–412, 2022. DOI: 10.56754/0719-0646.2403.0393. Disponível em: https://cubo.ufro.cl/ojs/index.php/cubo/article/view/3206. Acesso em: 4 may. 2024.