2013-04-10 23:57:08 -07:00
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empty(U-V) :-
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2014-01-17 05:32:22 +00:00
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unify_with_occurs_check(U, V).
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2013-04-10 23:57:08 -07:00
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push(Queue, Value, NewQueue) :-
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2014-01-17 05:32:22 +00:00
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append_dl(Queue, [Value|X]-X, NewQueue).
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2013-04-10 23:57:08 -07:00
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% when queue is empty pop fails.
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pop([X|V]-U, X, V-U) :-
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2014-01-17 05:32:22 +00:00
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\+empty([X|V]-U).
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2013-04-10 23:57:08 -07:00
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append_dl(X-Y, Y-Z, X-Z).
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