@Misc{ 
  Spe14,
  author = { Spector, Daniel },
  title = { $L^p$-Taylor approximations characterize the Sobolev space $W^{1,p}$ },
  journal = { C. R. Acad. Sci. Paris Sér. I Math },
  year = { 2014 },
  pages = { 7 },
  URL = { http://cvgmt.sns.it/paper/2450/ },
  note = { cvgmt preprint}
}