OMEL’CHENKO, P. V. On reduction of block matrices in a Hilbert space. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 61, n. 10, p. 1338–1347, 2009. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3105. Acesso em: 14 apr. 2025.