@Article{ 
  fraserser05a,
  author = { Franchi, Bruno and Serapioni, Raul and Serra Cassano, Francesco },
  title = { Intrinsic submanifolds, graphs and currents in Heisenberg groups },
  journal = { Lectures Notes of Seminario Interdisciplinare di Matematica },
  year = { 2005 },
  volume = { 4 },
  pages = { 23-38 },
  URL = { http://cvgmt.sns.it/paper/1409/ },
  note = { cvgmt preprint}
}