Approximation properties of the Vallée-Poussin means of partial sums of a special series in Laguerre polynomials (Q2666618)

Mixed series in Laguerre polynomials were introduced by \textit{I. I. Sharapudinov} [Sib. Math. J. 58, No. 2, 338--362 (2017; Zbl 1371.33023); translation from Sib. Mat. Zh. 58, No. 2, 440--467 (2017)]. Here the authors study approximative properties of the de la Vallée-Poussin means \[ \frac{1}{m+1}\sum_{k=n}^{n+m}S_{n+r}^{\alpha}(x) \] of their partial sums \( S_n^{\alpha}(x) \).