S. MAHMOOD, A.; E. ABD, M. The Simple Rings of Differential Operators. Journal of Education and Science (JES), [S. l.], v. 18, n. 4, p. 94–101, 2006. DOI: 10.33899/edusj.2006.77268. Disponível em: https://rjps.uomosul.edu.iq/edusj/article/view/18016. Acesso em: 4 aug. 2025.