Rusev, Peter. “Zeroes of Polynomials and Entire Functions in the Works of N. Obreshkoff”.
Ann. Sofia Univ. Fac. Math. and Inf.
89 (December 12, 1997): 37–46. Accessed April 18, 2025. https://annual.uni-sofia.bg/index.php/fmi/article/view/353.