NADLER, S. B. Periodic points of multi-valued $\varepsilon $-contractive maps. Topological Methods in Nonlinear Analysis, [S. l.], v. 22, n. 2, p. 399–409, 2003. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2003.048. Acesso em: 22 jul. 2024.