@Article{ 
  barservit06,
  author = { Barone Adesi, Vittorio and Serra Cassano, Francesco and Vittone, Davide },
  title = { The Bernstein problem for intrinsic graphs in Heisenberg groups and calibrations },
  journal = { Calc. Var. & PDEs },
  year = { 2007 },
  volume = { 30 },
  number = { 1 },
  pages = { 17-49 },
  URL = { http://cvgmt.sns.it/paper/737/ },
  note = { cvgmt preprint}
}