So what about the second clause, the recursive clause? This says that: The first clause (the escape clause, the one that is not recursive, or as we shall usually call it, the base clause), simply says that: And the declarative meaning of this recursive definition is fairly straightforward. ![]() That is, the declarative meaning of a Prolog knowledge base is simply “what it says”, or “what it means, if we read it as a collection of logical statements”. The word “declarative” is used to talk about the logical meaning of Prolog knowledge bases. ) Let’s now consider both the declarative and procedural meanings of this definition. (Significantly, the body of the first rule makes no mention of ![]() Predicate, which occurs in the first rule. Crucially, however, there is an ‘escape’ from this circularity. Is (at least partially) defined in terms of itself, for theįunctor occurs in both the head and body of the second rule. At first glance this seems pretty ordinary: it’s just a knowledge base containing three facts and two rules.
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