**Go up to** 6 Arc Consistency

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## Solution to part (a)

Is the arc *<X,Y>* arc consistent?
**no.**
Arc *<X,Y>* is arc consistent means that for every *X* there
exists a *Y* such that *r(X,Y)* is true.
The following table shows for each value of *X* a value of *Y* such
that *R(X,Y)* is true:

There is no element *Y* in *{a,d,i,r}* such that *r(c,Y)*
is true. That is there is no word starting with *ca*, *cd*, *ci*, or
*cr* in the word list. *c* can be removed from the domain of *X* to
make *<X,Y>* arc consistent.

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material, ©David Poole, Alan Mackworth and Randy Goebel, 1999