@Article{ 
  lousan11a,
  author = { Louet, Jean and Santambrogio, Filippo },
  title = { A sharp inequality for transport maps in $W^{1,p}(\mathbb{R})$ via approximation },
  journal = { Applied Math Letters },
  year = { 2012 },
  volume = { 25 },
  number = { 3 },
  pages = { 648-653 },
  URL = { http://cvgmt.sns.it/paper/1373/ },
  note = { cvgmt preprint}
}