CONRAD, P. Generalized Semigroup Rings. The Journal of the Indian Mathematical Society, [S. l.], v. 21, n. 1-2, p. 73–95, 1957. DOI: 10.18311/jims/1957/16973. Disponível em: https://www.informaticsjournals.com/index.php/jims/article/view/16973. Acesso em: 9 may. 2024.