RIBARSKA, N.; TSACHEV, T.; KRASTANOV, M. The intrinsic mountain pass principle. Topological Methods in Nonlinear Analysis, [S. l.], v. 12, n. 2, p. 309–322, 1998. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1998.044. Acesso em: 20 apr. 2024.