A substitution operation for constraints
In order to reduce the search space in finite constraint satisfaction problems, a number of different preprocessing schemes have been proposed. This paper introduces a ‘substitution’ operation for constraints. This new operation generalizes both the idea of enforcing consistency and the notion of label substitution introduced by Freuder. We show that the constraints in a problem may be replaced by substitutable subsets in order to simplify the problem without affecting the existence of a solution. Furthermore, we show how substitutability may be established locally, by considering only a subproblem of the complete problem.
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