PICCIONE, Paolo; TAUSK, Daniel 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/index.php/cubo/article/view/1718. Acesso em: 12 oct. 2025.