@Misc{ 
  butmin04,
  author = { Buttazzo, Giuseppe and Mintchev, Mihail },
  title = { Curve brachistocrone in campi di gravita' },
  journal = {  },
  year = { 2004 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/4/ },
  note = { cvgmt preprint}
}