  The natural proof of distribution in any proof system uses both weakening and contraction, so it is not available in the relevant logic \(\mathbf{R}\), which does not contain weakening. As a result, proof theories for \(\mathbf{R}\) either contain distribution as a primitive rule, or contain a second form of premise combination (so called extensional combination, as opposed to the intensional premise combination we have seen) which satisfies weakening and contraction. 