@Misc{ 
  bigser07,
  author = { Bigolin, Francesco and Serra Cassano, Francesco },
  title = { Intrinsic regular graphs in Heisenberg groups vs. weak solutions of non linear first-order PDEs },
  journal = { Adv. Calc. Var. },
  year = { 2009 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/281/ },
  note = { cvgmt preprint}
}