@Article{ 
  Mon13,
  author = { Monti, Roberto },
  title = { The regularity problem for sub-Riemannian geodesics },
  journal = { Springer INDAM Series },
  year = { 2013 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/2069/ },
  note = { cvgmt preprint}
}