ZhyhalloK. M., and KharkevychYu. I. “On the Approximation of Functions of the Hölder Class by Biharmonic Poisson Integrals”. Ukrains’kyi Matematychnyi Zhurnal 52, no. 7 (July 25, 2000): 971-974. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4496.