Agostino Cortesi Gilberto Filé William H. Winsborough Prop revisited: Propositional Formula as Abstract Domain for Groundness Analysis 322-327 conf/lics/LICS6 1991 conf/lics/1991 LICS db/conf/lics/lics91.html#CortesiFW91 http://dx.doi.org/10.1109/LICS.1991.151656