HALBERG, C. J. A. ,. Jr.; SAMUELSSON, A. On the Fine Structure of Spectra. Mathematica Scandinavica, Berkeley, CA, United States, v. 29, p. 37–49, 1971. DOI: 10.7146/math.scand.a-11032. Disponível em: https://journals.msp.org/mscand/article/view/2322. Acesso em: 25 jul. 2026.