Radzievskii, G. V. “Moduli of Continuity Defined by Zero Continuation of Functions and K-Functionals With Restrictions”. Ukrains’kyi Matematychnyi Zhurnal, vol. 48, no. 11, Nov. 1996, pp. 1537-54, https://umj.imath.kiev.ua/index.php/umj/article/view/5208.