Dyuzhenkova, O. Yu. “A Remark Concerning the Modulus of Smoothness Introduced by Ditzian and Totik”.
Ukrains’kyi Matematychnyi Zhurnal
, vol. 47, no. 12, Dec. 1995, pp. 1627–1638,
https://umj.imath.kiev.ua/index.php/umj/article/view/5556
.