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Finite domain (FD) constraints have become quite popular and are widely supported. A finite domain variable denotes an integer. However, we may not know exactly which integer. Typically we only know that it must be one of a finite number of possibilities, e.g. one of 1,2 or 7. This would be represented by a basic constraint:
Suppose, we have a second FD variable . If we unify them
, their domains are intersected thus resulting in the conclusion
. This technique underlies the efficient treatment of agreement: if
encodes the agreement information on one word and
on another and the 2 words must agree, then the constraint
enforces this agreement.
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