@Article{ 
  kirser03,
  author = { Kirchheim, Bernd and Serra Cassano, Francesco },
  title = { Rectifiability and parametrization of intrinsic regular surfaces in the Heisenberg group },
  journal = { Ann. Scuola Norm.Sup. Pisa Cl.Sci. (5) },
  year = { 2004 },
  volume = { III },
  pages = { 871-896 },
  URL = { http://cvgmt.sns.it/paper/7/ },
  note = { cvgmt preprint}
}