RAIMI, Ralph A. On a Theorem of E. Folner. Mathematica Scandinavica, Berkeley, CA, United States, v. 6, p. 47–49, 1958. DOI: 10.7146/math.scand.a-10535. Disponível em: https://journals.msp.org/mscand/article/view/2812. Acesso em: 25 jul. 2026.