PICCIONE, P.; TAUSK, D. V. Topological Methods for ODE’s: Symplectic Differential Systems. CUBO, A Mathematical Journal, [S. l.], v. 5, n. 1, p. 321–361, 2003. Disponível em: https://cubo.ufro.cl/ojs/index.php/cubo/article/view/1718. Acesso em: 19 may. 2024.