@Article{ 
  but06,
  author = { Buttazzo, Giuseppe },
  title = { Problems with Free Interfaces and Free Discontinuities: Variational Problems },
  journal = { Encyclopedia of Mathematical Physics (ISBN 978-0-1251-2666-3), Elsevier, Amsterdam (2006). },
  year = { 2006 },
  volume = { 2 },
  pages = { 411-416 },
  URL = { http://cvgmt.sns.it/paper/929/ },
  note = { cvgmt preprint}
}