@Article{ 
  leomas02,
  author = { Leonardi, Gian Paolo and Masnou, Simon },
  title = { On the isoperimetric problem in the Heisenberg group ${\mathbf{H^n}}$ },
  journal = { Annali di Mat. Pura Appl. },
  year = { 2005 },
  volume = { 184 },
  pages = { 533-553 },
  URL = { http://cvgmt.sns.it/paper/1357/ },
  note = { cvgmt preprint}
}