nLab
contraction rule

The contraction rule

Idea

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.

Statements

Exactly how this looks depends on the logic used.

Revised on January 20, 2014 01:44:04 by Urs Schreiber (89.204.139.46)