@Misc{ 
  BaGrMoRi19,
  author = { Baudoin, Fabrice and Grong, Erlend and Molino, Gianmarco and Rizzi, Luca },
  title = { Comparison theorems on H-type sub-Riemannian manifolds },
  journal = {  },
  year = { 2019 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/4454/ },
  note = { cvgmt preprint}
}