@Misc{ 
  BraPar14,
  author = { Brasco, Lorenzo and Parini, Enea },
  title = { The second eigenvalue of the fractional $p-$Laplacian },
  journal = { Adv. Calc. Var. },
  year = { 2015 },
  pages = { 37 },
  URL = { http://cvgmt.sns.it/paper/2522/ },
  note = { cvgmt preprint}
}