SPRADLIN, G. S. A Hamiltonian system with an even term. Topological Methods in Nonlinear Analysis, [S. l.], v. 10, n. 1, p. 93–106, 1997. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1997.023. Acesso em: 22 lip. 2024.