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called the body, and the Bi are called literals or conditions. When n = 0, the rule is called a fact and is written in the simplified form:

:A.

Queries (or goals) have the same syntax as the bodies of rules and are commonly written in the form:

:?- B1, ..., Bn.

In the simplest case of Horn clauses (or "definite" clauses), all of the A, B₁,

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