@Article{ 
  dinpalval11,
  author = { Di Nezza, Eleonora and Palatucci, Giampiero and Valdinoci, Enrico },
  title = { Hitchhiker's guide to the fractional Sobolev spaces },
  journal = { Bull. Sci. math. },
  year = { 2012 },
  volume = { 136 },
  number = { 5 },
  pages = { 521-573 },
  URL = { http://cvgmt.sns.it/paper/1385/ },
  note = { cvgmt preprint}
}