@Misc{ 
  dangarsal01,
  author = { Danielli, Donatella and Garofalo, Nicola and Salsa, Sandro },
  title = { Variational inequalities with lack of ellipticity. Part I: optimal interior regularity and non-degeneracy of the free boundary },
  journal = { Indiana University Math J },
  year = { 2001 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/59/ },
  note = { cvgmt preprint}
}