@Misc{ 
  BoaNalVit22,
  author = { Boarotto, Francesco and Nalon, Luca and Vittone, Davide },
  title = { The Sard problem in step 2 and in filiform Carnot groups },
  journal = {  },
  year = { 2022 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/5489/ },
  note = { cvgmt preprint}
}