@Article{ 
  BarRiz14,
  author = { Barilari, Davide and Rizzi, Luca },
  title = { Comparison theorems for conjugate points in sub-Riemannian geometry },
  journal = { Control, Optimisation and Calculus of Variations },
  year = { 2014 },
  doi = { 10.1051/cocv/2015013 },
  volume = { 22 },
  number = { 2 },
  pages = { 439 - 472 },
  URL = { http://cvgmt.sns.it/paper/2337/ },
  note = { cvgmt preprint}
}