Graph-null sets

Abstract

We say that a plane set $A$ is {\it graph-null,} if there is a function $g:[0,1]\to \mathbb{R}$ such that $\hat{I}{»}_2(A+\mathrm{graph}g)=0$. A plane set $A$ has the {\it translational Kakeya property} if, for every translated copy $A^{\prime }$ of $A$ and for every $\hat{I}\mu >0$, there is a finite sequence of vertical and horizontal translations bringing $A$ to $A^{\prime }$ such that the area touched during the horizontal translations is less than $\hat{I}\mu$. These properties are equivalent if $A$ is compact. We show that the graph of every absolutely continuous function is graph-null. Also, the graph of a typical continuous function is graph-null. Therefore, there are nowhere differentiable continuous functions whose graphs are graph-null. Still, we show that there exists a continuous function whose graph is not graph-null.