@Misc{ 
  buttre98,
  author = { Buttazzo, Giuseppe and Trebeschi, Paola },
  title = { The Role of Monotonicity in Some Shape Optimization Problems },
  journal = {  },
  year = { 1998 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/112/ },
  note = { cvgmt preprint}
}