@Misc{ 
  are,
  author = { Arena, Gabriella },
  title = { "Intrinsic Graphs, Convexity and Calculus on Carnot Groups" },
  journal = {  },
  year = { 2008 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/354/ },
  note = { cvgmt preprint}
}