Introduction to Prolog and Computational Linguistics -- Arity Differences

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Arity Differences

This happens for instance when you have decided to add another variable to a predicate definition because it is needed in a particular clause. You must remember to change all calls to the predicate. If you don't, the call will fail because the predicate is undefined.

What The Interpreter Says

(unless you are so unlucky that the misspelt word unifies with something else):

warns you that predicatename/arity is undefined.

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