GIROUARD, A. Relative homological linking in critical point theory. Topological Methods in Nonlinear Analysis, [S. l.], v. 30, n. 2, p. 211–221, 2007. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2007.026. Acesso em: 17 jan. 2022.