COHN, J. H. E. On $n$-Sum Groups. MATHEMATICA SCANDINAVICA, [S. l.], v. 75, p. 44–58, 1994. DOI: 10.7146/math.scand.a-12501. Disponível em: https://www.mscand.dk/article/view/12501. Acesso em: 14 apr. 2025.