STEINIG, B. On the essential maximality of linear operators in a Hilbert space. Annales Fennici Mathematici, [S. l.], v. 16, n. 1, p. 199–210, 1991. DOI: 10.5186/aasfm.1991.1627. Disponível em: https://afm.journal.fi/article/view/134716. Acesso em: 25 nov. 2024.