@Article{ 
  cupguimar07,
  author = { Cupini, Giovanni and Guidorzi, Marcello and Marcelli, Cristina },
  title = { Necessary conditions and non-existence results for autonomous nonconvex variational problems },
  journal = { J. Differential Equations },
  year = { 2007 },
  volume = { 243 },
  pages = { 329-348 },
  URL = { http://cvgmt.sns.it/paper/586/ },
  note = { cvgmt preprint}
}