ZhyhalloK. M., and KharkevychYu. I. “Approximation of (ψ, β)-Differentiable Functions of low Smoothness by Biharmonic Poisson Integrals”. Ukrains’kyi Matematychnyi Zhurnal 63, no. 12 (December 25, 2011): 1602-1622. Accessed November 22, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2829.