@Article{ 
  delsze,
  author = { De Lellis, Camillo and Székelyhidi, László Jr. },
  title = { Simple proof of two-well rigidity },
  journal = { C. R. Math. Acad. Sci. Paris },
  year = { 2006 },
  volume = { 343 },
  number = { 5 },
  pages = { 367-370 },
  URL = { http://cvgmt.sns.it/paper/263/ },
  note = { cvgmt preprint}
}