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Solution to part (b)

Is the arc <Y,X> arc consistent? yes. Arc <Y,X> is arc consistent means that for every Y there exists an X such that r(X,Y) is true. The following table shows for each value of Y a value of X such that R(X,Y) is true:
Thus the arc <Y,X> is arc consistent. The most common mistake: The relation r(X,Y) corresponds to two arcs, <X,Y> and <Y,X>. You do not swap the arguments to r(X,Y).
Computational Intelligence online material, ©David Poole, Alan Mackworth and Randy Goebel, 1999

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