Zhyhallo TV, Kharkevych YI. Approximation of functions from the class $\hat{C}^{\psi}_{\beta, \infty}$ by Poisson biharmonic operators in the uniform metric. Ukr. Mat. Zhurn. [Internet]. 2008 May 25 [cited 2025 Dec. 6];60(5):669 – 693. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/3185