@Article{ 
  ambmag02,
  author = { Ambrosio, Luigi and Magnani, Valentino },
  title = { Weak differentiability of BV functions on stratified groups },
  journal = { Math. Z. },
  year = { 2003 },
  volume = { 245 },
  pages = { 123-153 },
  URL = { http://cvgmt.sns.it/paper/782/ },
  note = { cvgmt preprint}
}