@Misc{ 
  monmor04,
  author = { Monti, Roberto and Morbidelli, Daniele },
  title = { Non tangentially accesible domains for vector fields },
  journal = { Indiana Univ. Math. J. },
  year = { 2004 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/1103/ },
  note = { cvgmt preprint}
}