HELSON, H.; SARASON, D. Past and Future. MATHEMATICA SCANDINAVICA, [S. l.], v. 21, p. 5–16, 1967. DOI: 10.7146/math.scand.a-10840. Disponível em: https://www.mscand.dk/article/view/10840. Acesso em: 4 may. 2024.