@Misc{ 
  BarFigRos17,
  author = { Barrios, Begoña and Figalli, Alessio and Ros-Oton, Xavier },
  title = { Global regularity for the free boundary in the obstacle problem for the fractional Laplacian },
  journal = { Amer. J. Math. },
  year = { 2017 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/3419/ },
  note = { cvgmt preprint}
}