Popivanov, Nedyu, and Todor Popov. “ESTIMATES FOR THE SINGULAR SOLUTIONS OF THE 3-D PROTTER’S PROBLEM”. Ann. Sofia Univ. Fac. Math. and Inf. 96 (December 12, 2004): 117–139. Accessed November 21, 2024. https://stipendii.uni-sofia.bg/index.php/fmi/article/view/167.