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p(X,Y) :- (p(X,Z) ^ !p(Z,Y))
p(X,Y) :- q(X,Y)
q(a,b) :- true
q(b,c) :- top

p(a,c) should be top.

p(a) :- top
p(b) :- bot
q :- !p(X)

q should be true but its false

Predicate symbols that are used in the rules but are do not appear in any rule's head are currently not supported in the tool. The tool must detect such predicate symbols define them (otherwise XSB throws an error).

Building policy
permit(Subject, cab) :- (daytime ^ employee(Subject))
permit(Subject, cab) :- (!daytime ^ employee(Subject) ^ validPin(Subject))

Office Policy
permit(Subject, cnb_f110) :- owns(Subject, cnb_f110)
permit(Subject, cnb_f110) :- delegate(SubjectA)@subject'

Stored on the card
owns(paul,cnb_f110) :- true
delegate(srdjan)@paul :- true

policynot(X,R) :- !policy(X,R)
policy(X,R) :- (poleval(X,R) -bot-> true)
poleval(ann,req) :- true
poleval(bob,req) :- false

policynot(bob,req) results in TOP, and not TRUE. The problem is fixed when the predicate policynot is renamed to something that does not contain "not".

Free variables in heads must not be allowed.

add support for atoms of the form contains(X,Y)@fs. This should be translated automatically to contains(fs, X, Y)