@Misc{ 
  pinval,
  author = { Pinamonti, Andrea and Valdinoci, Enrico },
  title = { A Lewy-Stampacchia Estimate for variational inequalities in the Heisenberg group },
  journal = { Rend.Istit.Mat.Univ.Trieste },
  year = { 2013 },
  volume = { 45 },
  pages = { 23--45 },
  URL = { http://cvgmt.sns.it/paper/552/ },
  note = { cvgmt preprint}
}