Steffensen's inequality

Steffensen's inequality is a result in mathematics related to the approximation of integrals and the estimation of the error in numerical integration. It provides bounds on the difference between the integral of a function and its numerical approximation using a specific technique, often involving Riemann sums or similar methods. The inequality can be stated as follows: Let \( f \) be a function that is monotonic on the interval \([a, b]\).