@Article{ 
  mag10,
  author = { Magnani, Valentino },
  title = { An area formula in metric spaces },
  journal = { Colloq. Math. },
  year = { 2011 },
  volume = { 124 },
  pages = { 275-283 },
  URL = { http://cvgmt.sns.it/paper/772/ },
  note = { cvgmt preprint}
}