May's Conjecture on Bimonoidal Functors and Multiplicative Infinite Loop Space Theory

A conjecture of May states that there is an up-to-adjunction strictification of symmetric bimonoidal functors between bipermutative categories. The main result of this paper proves a weaker form of May’s conjecture that starts with multiplicatively strong symmetric bimonoidal functors. As the main application, for May’s multiplicative infinite loop space machine from bipermutative categories to either E-infinity ring spaces or E-infinity ring spectra, multiplicatively strong symmetric bimonoidal functors can be replaced by strict symmetric bimonoidal functors.