RadzievskiiG. V. (1997) “On the best approximations and rate of convergence of decompositions in the root vectors of an operator”, Ukrains’kyi Matematychnyi Zhurnal, 49(6), pp. 754–773. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5060 (Accessed: 24November2024).