REDFIELD, R. H. Some properties of positive derivations on f-rings II. International Journal of Advanced Mathematical Sciences, [S. l.], v. 2, n. 3, p. 132–136, 2014. DOI: 10.14419/ijams.v2i3.3466. Disponível em: https://sciencepubco.com/index.php/IJAMS/article/view/3466.. Acesso em: 26 may. 2024.