FEI, G. Multiple periodic solutions of asymptotically linear Hamiltonian systems via Conley index theory. Topological Methods in Nonlinear Analysis, [S. l.], v. 23, n. 1, p. 89–114, 2004. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2004.005. Acesso em: 28 mar. 2024.