@Article{ 
  foca,
  author = { Focardi, Matteo },
  title = { Aperiodic fractional obstacle problems },
  journal = { Advances in Mathematics },
  year = { 2010 },
  volume = { 225 },
  pages = { 36 },
  URL = { http://cvgmt.sns.it/paper/779/ },
  note = { cvgmt preprint}
}