AUBERT, Karl Egil. On the ideal theory of commutative semi-groups. Mathematica Scandinavica, Berkeley, CA, United States, v. 1, p. 39–54, 1953. DOI: 10.7146/math.scand.a-10363. Disponível em: https://journals.msp.org/mscand/article/view/2959. Acesso em: 25 jul. 2026.