SCHECHTER, M.; TINTAREV, K. Nonlinear eigenvalues and mountain pass methods. Topological Methods in Nonlinear Analysis, [S. l.], v. 1, n. 2, p. 183–201, 1993. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1993.014. Acesso em: 3 jul. 2024.