@Misc{ 
  DePPra17,
  author = { De Philippis, Guido and Pratelli, Aldo },
  title = { The closure of planar diffeomorphisms in Sobolev spaces },
  journal = { Ann. Inst. H. Poincaré Anal. Non Linéaire },
  year = { 2019 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/3636/ },
  note = { cvgmt preprint}
}