@Misc{ 
  leorig01,
  author = { Leonardi, Gian Paolo and Rigot, Severine },
  title = { Isoperimetric sets in Carnot groups },
  journal = { Houston J. Math. },
  year = { 2002 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/1372/ },
  note = { cvgmt preprint}
}