Kalchuk, I. V., and Yu. I. Kharkevych. “I. Approximative Properties of Biharmonic Poisson Integrals in the Classes $W^r_{\beta} H^{\alpha}$”. Ukrains’kyi Matematychnyi Zhurnal 68, no. 11 (November 25, 2016): 1493-1504. Accessed February 29, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/1936.