LANCELOTTI, S. Nontrivial solutions of variational inequalities. The degenerate case. Topological Methods in Nonlinear Analysis, [S. l.], v. 18, n. 2, p. 303–319, 2001. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2001.036. Acesso em: 16 oct. 2021.