@Misc{ 
  frates,
  author = { Franchi, Bruno and Tesi, Maria Carla },
  title = { Wave and Maxwell's equations in Carnot groups },
  journal = {  },
  year = { 2010 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/193/ },
  note = { cvgmt preprint}
}