S. MAHMOOD, A. On the Rings of Differential Operators. AL-Rafidain Journal of Computer Sciences and Mathematics, [S. l.], v. 3, n. 1, p. 117–126, 2006. DOI: 10.33899/csmj.2006.164041 . Disponível em: https://csmj.uomosul.edu.iq/index.php/csmj/article/view/37080. Acesso em: 18 dec. 2025.