M. AL-BADAWI, L. Revising the cardinal vowel system on the basis of the set theory. Adab Al-Rafidayn, [S. l.], v. 23, n. 25, p. 29–39, 1993. DOI: 10.33899/radab.1993.165046. Disponível em: https://jamh.uomosul.edu.iq/index.php/radab/article/view/32577. Acesso em: 28 sep. 2025.