A Simple Proof of Zahorski's Description of Non-Differentiability Sets of Lipschitz Functions
Thomas Fowler, David Preiss · Real Analysis Exchange · 2009
We provide a simplification of Zahorski's argument showing that for every Lebesgue null $G_{\delta\sigma}$ subset $G$ of the line there is a Lipschitz function that is non-differentiable precisely at the points of $G$.