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For each of the following strings, say whether it is a syntactically legal expression in our query language.
| (a) |
goal(X) :- p(a,f(f(X))) |
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| (b) |
goal(X,Y) :- p(X,Y) & ~p(Y,X) |
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| (c) |
~goal(X,Y) :- p(X,Y) & p(Y,X) |
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| (d) |
goal(P,Y) :- P(a,Y) |
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| (e) |
goal(X) :- p(X,b) & p(X,p(b,c)) |
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