ALCÁNTARA BODE, Julio. A criteria of completeness for compact operators in Hilbert space. Pro Mathematica, [S. l.], v. 18, n. 35-36, p. 47–54, 2004. Disponível em: https://revistas.pucp.edu.pe/index.php/promathematica/article/view/10218. Acesso em: 24 dic. 2025.