DEAL, E. R. Quasi-Spectral Theory. Mathematica Scandinavica, Berkeley, CA, United States, v. 13, p. 188–198, 1963. DOI: 10.7146/math.scand.a-10698. Disponível em: https://journals.msp.org/mscand/article/view/2627. Acesso em: 25 jul. 2026.