OLESEN, Dorte. On Norm-Continuity and Compactness of Spectrum. Mathematica Scandinavica, Berkeley, CA, United States, v. 35, p. 223–236, 1974. DOI: 10.7146/math.scand.a-11549. Disponível em: https://journals.msp.org/mscand/article/view/2096. Acesso em: 25 jul. 2026.