H. ISMAIL, T.; O. HAMAD, I. A Nonstandard Generalization of Envelopes. AL-Rafidain Journal of Computer Sciences and Mathematics, [S. l.], v. 5, n. 2, p. 73–83, 2008. DOI: 10.33899/csmj.2008.163973 . Disponível em: https://csmj.uomosul.edu.iq/index.php/csmj/article/view/36973. Acesso em: 18 dec. 2025.