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In applications, QBF solvers are often required to generate strategies. This typically involves a process known as strategy extraction, where a Boolean circuit encoding a strategy is computed from a proof. It has previously been observed that Craig interpolation in propositional logic can be seen as a special case of QBF strategy extraction. In this paper we explore this connection further and show that, conversely, any strategy for a false QBF corresponds to a sequence of interpolants in its complete (Herbrand) expansion. Inspired by this correspondence, we present a new strategy extraction algorithm for the expansion-based proof system Exp+Res. Its asymptotic running time matches the best known bound of O(mn) for a proof with m lines and n universally quantified variables. We report on experiments comparing this algorithm with a strategy extraction algorithm based on combining partial strategies, as well as with round-based strategy extraction.
@InProceedings{slivovsky:LIPIcs.SAT.2024.28,
author = {Slivovsky, Friedrich},
title = {{Strategy Extraction by Interpolation}},
booktitle = {27th International Conference on Theory and Applications of Satisfiability Testing (SAT 2024)},
pages = {28:1--28:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-334-8},
ISSN = {1868-8969},
year = {2024},
volume = {305},
editor = {Chakraborty, Supratik and Jiang, Jie-Hong Roland},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SAT.2024.28},
URN = {urn:nbn:de:0030-drops-205509},
doi = {10.4230/LIPIcs.SAT.2024.28},
annote = {Keywords: QBF, Expansion, Strategy Extraction, Interpolation}
}
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