Zapryanova, Teodora, and Diko Souroujon. “Detailed Study on Characterization of Best Algebraic Approximation by a Generalized Modulus of Smoothness”. Theory and Practice of Mathematics and Computer Science Vol. 7 (February 12, 2021): 159–169. Accessed June 4, 2026. https://stm.bookpi.org/TPMCS-V7/article/view/164.