@Misc{ 
  lugmanstr02,
  author = { Lu, Guozhen and Manfredi, Juan and Stroffolini, Bianca },
  title = { Convex functions on the Heisenberg group },
  journal = { Calculus of Variations },
  year = { 2002 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/761/ },
  note = { cvgmt preprint}
}