ТРПЕНОВСКИ, Бранко Л. RECTANGULAR SEMIGROUPS. Matematichki Bilten, [S. l.], v. 29, n. 1, p. 99–104, 2005. Disponível em: https://bilten.smm.org.mk/index.php/bilten/article/view/1717. Acesso em: 14 aug. 2026.