@Misc{ 
  pinvala,
  author = { Pinamonti, Andrea and Valdinoci, Enrico },
  title = { A Geometric inequality for stable solutions of semilinear elliptic problems in the Engel group },
  journal = { Ann. Acad.Sci.Fenn.Math },
  year = { 2012 },
  number = { 37 },
  pages = { 357-373 },
  URL = { http://cvgmt.sns.it/paper/994/ },
  note = { cvgmt preprint}
}