@Article{ 
  pra04,
  author = { Pratelli, Aldo },
  title = { How to show that some rays are maximal transport rays in Monge problem },
  journal = { Rend. Sem. Mat. Univ. Padova },
  year = { 2005 },
  volume = { 113 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/76/ },
  note = { cvgmt preprint}
}