M. L. Gorbachuk and S. M. Torba, “On existence of boundary values of polyharmonic functions”, MFAT, vol. 10, no. 2, pp. 4–12, Jun. 2004, Accessed: Dec. 17, 2025. [Online]. Available: https://zen.imath.kiev.ua/index.php/mfat/article/view/236