DOROSHENKO, V. V. On semigroups of order-preserving transformations of countable linearly ordered sets. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 61, n. 6, p. 723–732, 2009. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3055. Acesso em: 6 dec. 2025.