Many problems can be expressed in terms of a numeric constraint satisfaction problem over finite or continuous domains (numeric CSP). The purpose of this paper is to show that the consistency techniques that have been developed for CSPs can be adapted to numeric CSPs. Since the numeric domains

(CSPs).

that guarantee that this database will be polynomial in the size of the problem in question. 1 INTRODUCTION The past few years have seen rapid progress in the development of algorithms for solving constraintsatisfaction problems, or csps. Csps arise naturally in subfields of AI from planning to vision

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Constraint Handling Rules (CHR) are our proposal to allow more flexibility and application-oriented customization of constraint systems. CHR are a declarative language extension especially designed for writing user-defined constraints. CHR are essentially a committed-choice language consisting of multi-headed guarded rules that rewrite constraints into simpler ones until they are solved. In this broad survey we aim at covering all aspects of CHR as they currently present themselves. Going from theory to practice, we will define syntax and semantics for CHR, introduce an important decidable property, confluence, of CHR programs and define a tight integration of CHR with constraint logic programming languages. This survey then describes implementations of the language before we review several constraint solvers - both traditional and non- standard ones - written in the CHR language. Finally we introduce two innovative applications that benefited from using CHR.

This paper introduces GRASP (Generic seaRch Algorithm for the Satisjiability Problem), an integrated algorithmic framework for SAT that un.$es several previously proposed searchpruning techniques and facilitates ident$cation of additional ones. GRASP is premised on the inevitability of confzicts during search and its most distinguishing feature is the augmentation of basic backtracking search with a powerfil confzict analysis procedure. Analyzing confzicts to determine their cawes enables GRASP to backtrack non-chronologically to earlier levels in the search tree, potentially pruning large portions of the search space. In addition, by “recording ” the causes of conflicts, GRASP can recognize andpreempt the occurrence of similar conficts later on in the search. Finally, straightjwward bookkeeping of the causality chains leading up to conflicts allows GRASP to identifi assignments that are necessary for a solution to be found. fiperimental results obtained from a large number of benchmarks, including many from the $eld of test pattern generation, indicate that application of the proposed confzict analysis techniques to SATalgorithm can be extremely effectivefor a large number of representative classes of SAT instances. 1

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with dynamic variable ordering is a very good algorithm for solving CSPs. 1 Introduction Despite ...