Abdullayev, F. G., and Yu. I. Kharkevych. 2020. “Approximation of the Classes $C^{\psi}_{\beta}H^{\alpha}$ by Biharmonic Poisson Integrals”. Ukrains’kyi Matematychnyi Zhurnal 72 (1), 20-35. https://umj.imath.kiev.ua/index.php/umj/article/view/1007.