KROM, Melven; KROM, Myren. Free Subgroups and Folners Conditions. MATHEMATICA SCANDINAVICA, [S. l.], v. 32, p. 242–244, 1973. DOI: 10.7146/math.scand.a-11458. Disponível em: https://www.mscand.dk/article/view/11458. Acesso em: 5 dec. 2025.