In logic, the *contraction rule* states that any valid deduction that uses a premise more than once remains valid using that premise only once. Along with the weakening rule and the exchange rule, it is one of the most commonly adopted structural rules.

The contraction rule is not used in all logical frameworks. For instance in linear logic it is discarded.

Exactly how this looks depends on the logic used.

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Last revised on January 20, 2014 at 01:44:04. See the history of this page for a list of all contributions to it.