@Misc{ 
  dangarnhi03,
  author = { Danielli, Donatella and Garofalo, Nicola and Nhieu, Duy-Minh },
  title = { Notions of convexity in Carnot groups },
  journal = { Comm. in Analysis and Geometry },
  year = { 2003 },
  volume = { 11 },
  number = { 2 },
  pages = { 263-341 },
  URL = { http://cvgmt.sns.it/paper/64/ },
  note = { cvgmt preprint}
}