Abdullayev, F. G., and Yu. I. Kharkevych. “Approximation of the Classes $C^{\psi}_{\beta}H^{\alpha}$ by Biharmonic Poisson Integrals”. Ukrains’kyi Matematychnyi Zhurnal 72, no. 1 (January 15, 2020): 20–35. Accessed December 5, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/1007.