SAMOILENKO, Yu. S.; GRUSHEVOI, R. V. Systems of one-dimensional subspaces of a Hilbert space. Methods of Functional Analysis and Topology, [S. l.], v. 16, n. 2, p. 131–139, 2010. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/446. Acesso em: 16 dec. 2025.