1% From Baral Book pg 81
    2eligible(X) :- highGPA(X).
    3eligible(X) :- special(X), fairGPA(X).
    4-eligible(X) :- -special(X), -highGPA(X).
    5interview(X) :- not eligible(X), not -eligible(X).
    6fairGPA(john).
    7-highGPA(john).
    8?- interview(john).