A unifying framework for tractable constraints
Many combinatorial search problems may be expressed as constraint satisfaction problems, and this class of problems is known to be NP-complete in general. In this paper we examine restricted classes of constraints which lead to tractable problems. We show that all known classes with this property may be characterized by a simple algebraic closure condition. Using this condition provides a uniform test to establish whether a given set of constraints falls into any of the known tractable classes, and may therefore be solved efficiently.
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