A Plethysm Formulation for Operadic Structures and its Relationship to the Plus Construction

We first introduce several families of monoidal categories with plethysm products as their monoidal products and use this to describe operadic structures as plethysm monoids. In order to link this approach with the classical theory, we give a generalization of the Baez-Dolan plus construction. We then show that an operadic structure can be defined as a plethysm monoid if its associated Feynman category is a plus construction of a unique factorization category.