HrabovaU. Z., KalchukI. V., & StepanyukT. A. (2018). On the approximation of the classes $W_{β}^rH^{α}$ by biharmonic Poisson integrals. Ukrains’kyi Matematychnyi Zhurnal, 70(5), 625-634. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/1582