DEAL, E. R. A Quasi-Spectral Operator. MATHEMATICA SCANDINAVICA, [S. l.], v. 16, p. 29–32, 1965. DOI: 10.7146/math.scand.a-10744. Disponível em: https://www.mscand.dk/article/view/10744. Acesso em: 2 may. 2024.