Serdyuk А. S.; Stepaniuk Т. Estimates of the best orthogonal trigonometric approximations of the classes of convolutions of periodic functions of not high smoothness . Reports of the National Academy of Sciences of Ukraine, Kyiv, Ukraine, n. 7, p. 13–19, 2025. DOI: 10.15407/dopovidi2015.07.013. Disponível em: https://nasu-periodicals.org.ua/index.php/dp/article/view/15066. Acesso em: 3 jun. 2025.