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Complexity of Clausal Constraints Over Chains
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Complexity of Clausal Constraints Over Chains
Nadia Creignou1 , Miki Hermann2 , Andrei Krokhin3 and Gernot Salzer4 
| (1) |
LIF (CNRS, UMR 6166), Univ. de la Méditerranée, 13288 Marseille cedex 9, France |
| (2) |
LIX (CNRS, UMR 7161), École Polytechnique, 91128 Palaiseau cedex, France |
| (3) |
Department of Computer Science, University of Durham, Durham, DH1 3LE, UK |
| (4) |
Technische Universität Wien, Favoritenstraße 9-11, 1040 Vienna, Austria |
Published online: 28 September 2007
Abstract
We investigate the complexity of the satisfiability problem of constraints over finite totally ordered domains. In our context,
a clausal constraint is a disjunction of inequalities of the form x≥ d and x≤ d. We classify the complexity of constraints based on clausal patterns. A pattern abstracts away from variables and contains
only information about the domain elements and the type of inequalities occurring in a constraint. Every finite set of patterns
gives rise to a (clausal) constraint satisfaction problem in which all constraints in instances must have an allowed pattern.
We prove that every such problem is either polynomially decidable or NP-complete, and give a polynomial-time algorithm for
recognizing the tractable cases. Some of these tractable cases are new and have not been previously identified in the literature.
Keywords Constraint satisfaction problems - Complexity - Finite totally ordered domains - Inequalities - Clausal patterns - Dichotomy theorem
The work has been supported by ÉGIDE 06606ZF, ÖAD Amadeus 18/2004, and by UK EPSRC grants EP/C543831/1 and EP/C54384X/1.
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