The plus construction was introduced by Baez-Dolan as a means for defining their notion of an opetope and by another name with another intent by Getzler and Kapranov. The plus construction has since proven to be a key component in different operadic theories such as the Feynman categories of Kaufmann and Ward. In this talk, I will discuss joint work with Ralph Kaufmann where we generalize the plus constructions to an endofunctor of symmetric monoidal categories. A special case is given by unique factorization categories whose plus construction yields Feynman categories. As an upshot, we can use this to connect the plus construction to monoid definitions of operad-like structures.
This is NOT Quillen's plus construction