On Boundary Values of Three-Harmonic Poisson Integral on the Boundary of a Unit Disk

The use of the isometry of function spaces with different numbers of variables in the theory of approximation of functions

“…In the case f ∈ L n , and T σ n ∈ F X n σ , we have, in view of the relations ( 8) and (9), that the function T σ n ∈ F C n σ , and from (14) get that ( f * T σ n ) is e.f.e.t.n.g. σ n .…”

“…Note that approximative properties of 2π-periodic analogs of these kernels were considered in the papers [9,10]. Denote by…”