“Order Estimates of Functionals in Terms of Which the Best $n$-Term Approximations of Classes ${\cal F}_{q,r}^{\psi}$ Are Expressed”. Transactions of Institute of Mathematics, the NAS of Ukraine, vol. 11, no. 3, June 2014, pp. 287-14, https://trim.imath.kiev.ua/index.php/trim/article/view/82.