BABENKO, V.F.; PARFINOVYCH, N.V.; SKOROKHODOV, D.S. The best approximation of closed operators by bounded operators in Hilbert spaces: Array. Carpathian Mathematical Publications, [S. l.], v. 14, n. 2, p. 453–463, 2022. DOI: 10.15330/cmp.14.2.453-463. Disponível em: https://journals.pnu.edu.ua/index.php/cmp/article/view/6161. Acesso em: 29 mar. 2024.