PERERA, K.; SCHECHTER, M. Multiple nontrivial solutions of elliptic semilinear equations. Topological Methods in Nonlinear Analysis, [S. l.], v. 16, n. 1, p. 1–15, 2000. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2000.027. Acesso em: 22 jul. 2024.