@Misc{ 
  PonSpe18,
  author = { Ponce, Augusto and Spector, Daniel },
  title = { A decomposition by non-negative functions in the Sobolev space $W^{k, 1}$ },
  journal = {  },
  year = { 2018 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/3942/ },
  note = { cvgmt preprint}
}