Dragomir, S.S., and A. Sofo. “Lower and Upper Bounds of the Čebyšev Functional for the Riemann-Stieltjes Integral”. Italian Journal of Pure and Applied Mathematics 28 (July 19, 2011): 41–50. Accessed July 18, 2026. https://journals.uniurb.it/index.php/ijpam/article/view/6017.