Roberto Bagnara Patricia M. Hill Elena Mazzi Enea Zaffanella Widening Operators for Weakly-Relational Numeric Abstractions. 3-18 2005 conf/sas/2005 SAS http://dx.doi.org/10.1007/11547662_3 db/conf/sas/sas2005.html#BagnaraHMZ05