@Misc{ 
  MagMar13,
  author = { Magnanini, Rolando and Marini, Michele },
  title = { Characterization of ellipsoids as $K$-dense sets },
  journal = {  },
  year = { 2013 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/2315/ },
  note = { cvgmt preprint}
}