Yefimushkin, A. S. “On Multivalent Solutions of the Riemann–Hilbert Problem in Multiply Connected Domains”. Reports of the National Academy of Sciences of Ukraine, no. 8 (August 28, 2016): 7–11. Accessed August 1, 2026. https://nasu-periodicals.org.ua/index.php/dp/article/view/11280.