Eliminating positive-measure level sets by small Lipschitz perturbations

Abstract

We establish a new regularity phenomenon of continuous functions. Specifically, given any continuous function $f$ and arbitrary $ε>0$, we construct a Lipschitz perturbation $g_ε$ whose Lipschitz seminorm is less than $ε$ such that every level set of $f+g_ε$ has Lebesgue measure zero.