LONG, Y. A Maslov-type index theory for symplectic paths. Topological Methods in Nonlinear Analysis, [S. l.], v. 10, n. 1, p. 47–78, 1997. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1997.021. Acesso em: 22 jul. 2024.