TOICHKINA, E. A. Semigroups of endotopisms of efficient and connected relations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 68, n. 3, p. 377–387, 2016. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/1845. Acesso em: 5 dec. 2025.