@Misc{ 
  mon10,
  author = { Monti, Roberto },
  title = { Rearrangements in metric spaces and in the Heisenberg group },
  journal = { J. Geom. Anal. },
  year = { 2013 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/1416/ },
  note = { cvgmt preprint}
}