MATTILA, Kristi. On proper boundary points of the spectrum and complemented eigenspaces. Mathematica Scandinavica, Berkeley, CA, United States, v. 43, p. 363–368, 1978. DOI: 10.7146/math.scand.a-11790. Disponível em: https://journals.msp.org/mscand/article/view/1856. Acesso em: 25 jul. 2026.