@Article{ 
  paoste05,
  author = { Paolini, Emanuele and Stepanov, Eugene },
  title = { Optimal transportation networks as flat chains },
  journal = { Interfaces and Free Boundaries },
  year = { 2006 },
  volume = { 8 },
  pages = { 393-436 },
  URL = { http://cvgmt.sns.it/paper/1394/ },
  note = { cvgmt preprint}
}