HÖRMANDER, L.; MELIN, A. A Remark on Perturbations of Compact Operators. MATHEMATICA SCANDINAVICA, [S. l.], v. 75, p. 255–262, 1994. DOI: 10.7146/math.scand.a-12518. Disponível em: https://www.mscand.dk/article/view/12518. Acesso em: 5 may. 2024.