GALE, D.; KLEE, V. Unique reducibility of subsets of commutative topological groups and semigroups. MATHEMATICA SCANDINAVICA, [S. l.], v. 36, p. 174–198, 1975. DOI: 10.7146/math.scand.a-11570. Disponível em: https://www.mscand.dk/article/view/11570. Acesso em: 7 may. 2024.