@inproceedings{BK07, author = "T. Ball and O. Kupferman", title = "Better Under-approximation of Programs by Hiding of Variables", booktitle = "Proc. 8th International Conference on Verification, Model Checking, and Abstract Interpretation", series = "Lecture Notes in Computer Science", publisher = "Springer-Verlag", year = "2007", volume = "4349", pages = "314-328" }