GALEWSKI, Marek; NOWAKOWSKI, Andrzej. Existence of solutions for a nonlinear wave equation. Topological Methods in Nonlinear Analysis, [S. l.], v. 28, n. 2, p. 385–399, 2006. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2006.034. Acesso em: 8 jul. 2025.