Shydlich AL. Order equalities for some functionals and their application to the estimation of the best $n$-term approximations and widths. Ukr. Mat. Zhurn. [Internet]. 2009Oct.25 [cited 2024Nov.22];61(10):1403-2. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/3110