@Misc{ 
  ambrig,
  author = { Ambrosio, Luigi and Rigot, Severine },
  title = { Optimal Mass Transportation in the Heisenberg Group },
  journal = { Journal of Functional Analysis },
  year = { 2002 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/1042/ },
  note = { cvgmt preprint}
}