Grabova, U. Z. “Approximation of the Classes of Convolutions of Periodic Functions by Zygmund Sums in Integral Metrics”. Reports of the National Academy of Sciences of Ukraine, no. 9 (September 28, 2014): 13–18. Accessed June 20, 2026. https://nasu-periodicals.org.ua/index.php/dp/article/view/16677.