@Misc{ 
  FocSpa19,
  author = { Focardi, Matteo and Spadaro, Emanuele },
  title = { The local structure of the free boundary in the fractional obstacle problem },
  journal = { Advances in Calculus of Variations },
  year = { 2019 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/4257/ },
  note = { cvgmt preprint}
}