@inproceedings{HagueOng2007,
  title = "Symbolic Backwards Reachability Analysis for Higher-Order Pushdown Systems",
  author = "M. Hague and C.-H. L. Ong",
  year = "2007",
  booktitle = "FoSSaCS",
  note = "<a href="http://www.comlab.ox.ac.uk/people/matthew.hague/FoSSaCS07-long.pdf">Long Version (pdf)</a>",
}