@PhdThesis{Bal05,
  author = {Ballis, D.},
  title = {{Rule-based Software Verification and Correction}},
  school = {Universidad Polit\'ecnica de Valencia and
  Universit\`a degli Studi di Udine},
  year = {2005},
  OPTmonth = {February},
  OPTnote = {This PhD thesis was done under a co-operation
  agreement (\emph{cotutela}) between the two universities}
}