LI, S. A new Morse theory and strong resonance problems. Topological Methods in Nonlinear Analysis, [S. l.], v. 21, n. 1, p. 81–100, 2003. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2003.005. Acesso em: 28 mar. 2024.