YUSENKO, K. A. On quadruples of projectors connected by a linear relation. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 58, n. 9, p. 1289–1295, 2006. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3531. Acesso em: 6 dec. 2025.