@Misc{ 
  ambmal05,
  author = { Ambrosio, Luigi and Malý, Jan },
  title = { Very weak notions of differentiability },
  journal = {  },
  year = { 2005 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/75/ },
  note = { cvgmt preprint}
}