ABEL, M. On Pullbacks of Abelian Groups and Pushouts of Rings. Communications in Mathematics and Applications, [S. l.], v. 3, n. 1, p. 1–8, 2012. DOI: 10.26713/cma.v3i1.139. Disponível em: https://www.rgnpublications.com/journals/index.php/cma/article/view/139. Acesso em: 29 apr. 2024.