@Misc{ 
  AmbRaj11,
  author = { Ambrosio, Luigi and Rajala, Tapio },
  title = { Slopes of Kantorovich potentials and existence of optimal transport maps in metric measure spaces },
  journal = { Ann. Mat. Pura Appl. },
  year = { 2012 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/1693/ },
  note = { cvgmt preprint}
}