Hrabova, U.Z., and I.V. Kal'chuk. “Approximation of the Classes $W^{r}_{\beta,\infty}$ by Three-Harmonic Poisson Integrals”. Carpathian Mathematical Publications 11, no. 2 (December 31, 2019): 321–334. Accessed November 22, 2024. https://vps.pnu.edu.ua/index.php/cmp/article/view/2111.