VOLKOVA, M. G.; GUBREEV, G. M. One remark about the unconditional exponential bases and cosine bases, connected with them. Methods of Functional Analysis and Topology, [S. l.], v. 14, n. 4, p. 330–333, 2008. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/396. Acesso em: 16 dec. 2025.