RAMM, A. G. A characterization of Unbounded Fredholm Operators. CUBO, A Mathematical Journal, [S. l.], v. 5, n. 3, p. 91–95, 2003. Disponível em: https://cubo.ufro.cl/ojs/index.php/cubo/article/view/1667. Acesso em: 19 may. 2024.