ABBONDANDOLO, A. A new cohomology for the Morse theory of strongly indefinite functionals on Hilbert spaces. Topological Methods in Nonlinear Analysis, [S. l.], v. 9, n. 2, p. 325–382, 1997. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1997.017. Acesso em: 17 jan. 2022.