@Article{ 
  monservit08,
  author = { Monti, Roberto and Serra Cassano, Francesco and Vittone, Davide },
  title = { A negative answer to the Bernstein problem for intrinsic graphs in the Heisenberg group },
  journal = { Boll. Unione Mat. Ital. (9) },
  year = { 2008 },
  volume = { 1 },
  number = { 3 },
  pages = { 709-727 },
  URL = { http://cvgmt.sns.it/paper/1123/ },
  note = { cvgmt preprint}
}