Zhyhallo, K. M., & Kharkevych, Y. I. (2011). Approximation of functions from the classes $C^{\psi}_{\beta, \infty}$ by biharmonic Poisson integrals. Ukrains’kyi Matematychnyi Zhurnal, 63(7), 939-959. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/2776