PečarićJ. E., PerušićA., and SmoljakK. “Generalizations of Steffensen’s Inequality by Lidstone’s Polynomials”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 67, no. 11, Nov. 2015, pp. 1525-39, http://umj.imath.kiev.ua/index.php/umj/article/view/2087.