@Misc{ 
  monmor,
  author = { Monti, Roberto and Morbidelli, Daniele },
  title = { John domains for the control distance of diagonal vector fields },
  journal = { Jour. Anal. Math. },
  year = { 2003 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/1251/ },
  note = { cvgmt preprint}
}