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derived rule

A shortcut rule that could always be replaced by basic-rule steps.

A derived rule is a rule that is not part of the basic proof system but can be justified by a proof in the basic system. Using it never lets you prove anything the basic rules could not.

Examples

  • Modus tollens (MT), disjunctive syllogism (DS), double negation elimination (DNE), and De Morgan (DeM) are derived rules in this course.

See also

rule of inference formal proof
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