Regular Points of a Subcartesian Space
  We discuss properties of the regular part $S_{reg}$ of a subcartesian space $S$. We show that $S_{reg}$ is open and dense in $S$ and the restriction to $S_{reg}$ of the tangent bundle of $S$ is locally trivial. 
Tsasa Lusala, J\c{e}drzej \'Sniatycki and Jordan Watts