On Derivatives Vanishing Almost Everywhere on Certain Sets

Abstract

Let \(g\) be a measurable real valued function on a bounded, measurable subset of the real line. We prove that if \(g(E)\) has measure 0, then 0 is one of the derived numbers of \(g\) at almost every point in \(E\). We find a function \(H\) on the real line that is nondecreasing and closely associated with \(G\), such that if \(g(E)\) has measure 0, the \(H'\) vanishes almost everywhere. Moreover, if \(g\) is an \(N\)-function on \(E\) and if \(H'\) vanishes almost everywhere, then \(g(E)\) has measure 0.