negation by failure

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negation by failure

An extralogical feature of Prolog and other logic programming languages in which failure of unification is treated as establishing the negation of a relation. For example, if Ronald Reagan is not in our database and we asked if he was an American, Prolog would answer "no".
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But there are cases when the circularity of the above description of negation as failure makes it confusing.
His argumentation systems can formalize and make inference on default reasoning, autoepistemic reasoning, theory formation, circumscription, negation as failure, and assumption-based reasoning.
Defeasible logic versus logic programming without negation as failure.