Multicategories from Symmetric Monoidal Categories

Abstract

This paper considers the possible underlying multicategories for a symmetric monoidal category, and shows that, up to canonical and coherent isomorphism, there really is only one. As a result, there is a well-defined forgetful functor from symmetric monoidal categories to multicategories, as long as all morphisms of symmetric monoidal categories are at least lax symmetric monoidal. The paper also shows that this forgetful functor has a weak left adjoint, and that the monad of the adjunction gives a strictification construction.

Revised following referee's report, and slightly reorganized from previous version