DOMAR, Yngve. A Theorem of Beurling-Helson Type. Mathematica Scandinavica, Berkeley, CA, United States, v. 33, p. 139–144, 1973. DOI: 10.7146/math.scand.a-11479. Disponível em: https://journals.msp.org/mscand/article/view/2183. Acesso em: 25 jul. 2026.