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Deduction may refer to a method by which inference is performed, or to a data structure stored in the Cyc KB.

Inference method: Deduction in Cyc uses two rules of inference. The first is, “If P implies Q, and P is known to be true, then Q is also true.” The second is, “If P implies Q, and Q is known to be false, then P is also false.” These rely on a particular meaning of “P implies Q”, namely that it is impossible for both P to be true and Q to be false.

Data structure: A deduction is an argument supporting a deduced assertion. It is composed of a justification that lists all the premises (assertions, including one rule) that entail the inferred assertion.