COTI ZELATI, V.; RABINOWITZ, P. H. Heteroclinic solutions between stationary points at different energy levels. Topological Methods in Nonlinear Analysis, [S. l.], v. 17, n. 1, p. 1–21, 2001. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2001.001. Acesso em: 4 feb. 2023.