Leviatan D, Motorna OV, Shevchuk IA. No Jackson-type estimates for piecewise $q$-monotone, $q\ge3$, trigonometric approximation. Ukr. Mat. Zhurn. [Internet]. 2022Jun.17 [cited 2024Apr.25];74(5):662 -75. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/7081