Ugolʹnikov, A.P. and Bekker, M.B. (2004) “The Helson-Szegö theorem for operator-valued weight”, Methods of Functional Analysis and Topology, 10(3), pp. 11–16. Available at: https://zen.imath.kiev.ua/index.php/mfat/article/view/248 (Accessed: 18 December 2025).