FOLNER, Erling. Note on a generalization of a theorem of Bogolioùboff. Mathematica Scandinavica, Berkeley, CA, United States, v. 2, p. 223–225, 1954. DOI: 10.7146/math.scand.a-10408. Disponível em: https://journals.msp.org/mscand/article/view/2912. Acesso em: 25 jul. 2026.