EKELAND, I. Some lemmas about dynamical systems. MATHEMATICA SCANDINAVICA, [S. l.], v. 52, p. 262–268, 1983. DOI: 10.7146/math.scand.a-12005. Disponível em: https://www.mscand.dk/article/view/12005. Acesso em: 1 may. 2024.