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Keywords:
distance function; WDC set; DC function; DC aura; Borel complexity
Summary:
We study WDC sets, which form a substantial generalization of sets with positive reach and still admit the definition of curvature measures. Main results concern WDC sets $A\subset {\mathbb R}^2$. We prove that, for such $A$, the distance function $d_A= {\rm dist}(\cdot,A)$ is a ``DC aura'' for $A$, which implies that each closed locally WDC set in ${\mathbb R}^2$ is a WDC set. Another consequence is that compact WDC subsets of ${\mathbb R}^2$ form a Borel subset of the space of all compact sets.
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