KolesnikL. I. and AndrashkоM. I. (1970) “Inverse theorems of approximation on the average in regions with angles”, Ukrains’kyi Matematychnyi Zhurnal, 23(1), pp. 97-104. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/8487 (Accessed: 24November2024).