Zhyhallo, K. M., and Yu. I. Kharkevych. “Approximation of Conjugate Differentiable Functions by Biharmonic Poisson Integrals”. Ukrains’kyi Matematychnyi Zhurnal 61, no. 3 (March 25, 2009): 333-345. Accessed April 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3023.