@inproceedings{BK08,
        author      =   "T. Ball and O. Kupferman",
        title       =   "Vacuity in testing",
        booktitle  =    "Proc.  2nd International Conference on Tests and Proofs",
        series      =   lncs,
        publisher   =   springer,
        year        =   "2008",
        volume      =   "4966",
        pages       =   "4--17"
}