ELIN, M.; SHOIKHET, D.; LAWRENCE, Z. A flower structure of backward flow invariant domains for semigroups. Annales Fennici Mathematici, [S. l.], v. 33, n. 1, p. 3–34, 2008. Disponível em: https://afm.journal.fi/article/view/135214. Acesso em: 12 may. 2024.