@Misc{ 
  BelLeD19,
  author = { Bellettini, Costante and Le Donne, Enrico },
  title = { Sets with constant normal in Carnot groups: properties and examples },
  journal = {  },
  year = { 2019 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/4506/ },
  note = { cvgmt preprint}
}