HAMIDOUNE, Y. O.; RÖDSETH, Ö. J. On Bases for $\sigma$-Finite Groups. Mathematica Scandinavica, Berkeley, CA, United States, v. 78, p. 246–254, 1996. DOI: 10.7146/math.scand.a-12586. Disponível em: https://journals.msp.org/mscand/article/view/1041. Acesso em: 25 jul. 2026.