@Article{ 
  magmugser06,
  author = { Magrone, Paola and Mugnai, Dimitri and Servadei, Raffaella },
  title = { Multiplicity of solutions for semilinear variational inequalities via linking and $\nabla$-theorems },
  journal = { J. Differential Equations },
  year = { 2006 },
  volume = { 228 },
  number = { 1 },
  pages = { 191-225 },
  URL = { http://cvgmt.sns.it/paper/389/ },
  note = { cvgmt preprint}
}