We characterize the closed sets in Euclidean space that satisfy a two-sided rolling ball property. As an application we show that certain conformal metric ratios have boundary value~1.
"Blaschke's rolling ball property and conformal metric ratios." Rocky Mountain J. Math. 47 (1) 161 - 184, 2017. https://doi.org/10.1216/RMJ-2017-47-1-161