Current numerical constraint propagation systems accept as input only problems represented by exact numerical values and correspondingly produce only crisp solutions as output. In order to remove this limitation we have designed and implemented a generalized constraint propagation scheme based on interval arithmetic instead of conventional arithmetic. By using intervals instead of exact values we may express inexact numerical constraints in a well-defined way and compute necessary conditions

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... consistency in inconsistent underconstrained or overconstrained situations. If only singleton intervals are used our system produces similar results as conventional exact value systems.