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In this paper, we investigate "gap problems", which are promise problems where YES instances are flexibly satisfiable in a certain sense, and NO instances are not satisfiable at all. These gap problems generalise a family of constraint-related decision problems, including the constraint satisfaction problem itself, the separation problem (can distinct variables be validly assigned distinct values?) and the 2-robust satisfiability problem (does any assignment on two variables extend to a full satisfying assignment?). We establish a Gap Trichotomy Theorem, which on Boolean domains, completely classifies the complexity of the gap problems considered. As a consequence, we obtain several well-known dichotomy results, as well as dichotomies for the separation problem and the 2-robust satisfiability problem: all are either polynomial-time tractable or NP-complete. Schaefer’s original dichotomy is a notable particular case.
@InProceedings{ham:LIPIcs.ISAAC.2016.36,
author = {Ham, Lucy},
title = {{A Gap Trichotomy for Boolean Constraint Problems: Extending Schaefer's Theorem}},
booktitle = {27th International Symposium on Algorithms and Computation (ISAAC 2016)},
pages = {36:1--36:12},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-026-2},
ISSN = {1868-8969},
year = {2016},
volume = {64},
editor = {Hong, Seok-Hee},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ISAAC.2016.36},
URN = {urn:nbn:de:0030-drops-68060},
doi = {10.4230/LIPIcs.ISAAC.2016.36},
annote = {Keywords: Constraint Satisfaction Problem, Robust satisfiability, Clone theory, Dichotomy, Trichotomy, Boolean}
}