@Article{ 
  ambpra,
  author = { Ambrosio, Luigi and Pratelli, Aldo },
  title = { Existence and stability results in the $L^1$ theory of optimal transportation },
  journal = {  },
  year = { 2002 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/1090/ },
  note = { cvgmt preprint}
}