YATUBA, Kozo. A note on functions with a spectral gap. Mathematica Scandinavica, Berkeley, CA, United States, v. 36, p. 279–285, 1975. DOI: 10.7146/math.scand.a-11577. Disponível em: https://journals.msp.org/mscand/article/view/2035. Acesso em: 25 jul. 2026.