Extended Failed-Literal Preprocessing for Quantified Boolean Formulas

ion makes Φ “truer” (more tree models). Pure existential literal rule makes Φ “falser” (fewer tree models). Pure universal literal rule makes Φ “falser” (fewer tree models). Unit-clause propagation and universal reduction do not change the set of tree models. So ? ? ? If abstraction changes u from universal to existential, and then it becomes pure, making it true is the wrong idea. Say u is assigned true due to purity. u cannot imply anything by unit propagation. But u can make some universal literal, say v, become pure. This combination is unsound. Experimental Results (more details in proceedings) Extended QxBF adds 1-saturation with pure universal literal rule to QxBF. Combine exqbf and bloqqer (Biere, Seidl, Lonsing, CADE 2011). Run multiple rounds so bloqqer can digest exqbf results. depqbf is the back-end solver. 0 200 400 600 80