SOLIMINI, S. Min-max levels on the double natural constraint. Topological Methods in Nonlinear Analysis, [S. l.], v. 28, n. 2, p. 319–333, 2006. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2006.032. Acesso em: 25 apr. 2024.