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Stage 1

Suppose that we have these (and only these) facts about knows/2.


knows(alf,bert). [-5pt]

How do we find all the solutions of the form knows(X,Y)? Now the goal knows(X,Y) is equivalent to asking ``does there exist some X and some Y such that knows(X,Y)''. For all solutions we want to ask something like ``for what set of values of X and set of values of Y is it true that for all X and all Y then knows(X,Y)''.

Z = [[jim,fred],[alf,bert]] [-5pt]

where Z is the set of all solution pairs [X,Y] such that knows(X,Y).

Paul Brna
Mon May 24 20:14:48 BST 1999