TARSKI, A. Remarks on direct products of commutative semigroups. MATHEMATICA SCANDINAVICA, [S. l.], v. 5, p. 218–223, 1957. DOI: 10.7146/math.scand.a-10497. Disponível em: https://www.mscand.dk/article/view/10497. Acesso em: 29 apr. 2024.