@Article{ 
  ste06,
  author = { Stepanov, Eugene },
  title = { Partial geometric regularity of some optimal connected transportation networks },
  journal = { J. Math. Sci. (N.Y.) },
  year = { 2006 },
  volume = { 132 },
  number = { 4 },
  pages = { 522-552 },
  URL = { http://cvgmt.sns.it/paper/314/ },
  note = { cvgmt preprint}
}