@Article{ 
  San17a,
  author = { Santilli, Mario },
  title = { Rectifiability and approximate differentiability of higher order for  sets },
  journal = { Indiana Univ. Math. J },
  year = { 2019 },
  doi = { 10.1512/iumj.2019.68.7645 },
  volume = { 68 (2019) },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/4762/ },
  note = { cvgmt preprint}
}