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Solution to part (b)
Is the arc <Y,X> arc consistent?
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).
material, ©David Poole, Alan Mackworth and Randy Goebel, 1999