Best approximation by “angles” of analytic in the unit bidisk functions

Abstract

Exact in some sense inequalities of the best approximation by ''angles'' $ $, have been obtained for the classes $\mathfrak{B}^{r_1,r_2}_2 (U^2), r_1, r_2 \in \mathbb{N}$, of two complex variables functions analytic in the unit bicircle $U^2$. These results are the application of Kolmogorov type inequalities for some problems of the approximation theory of functions.