Cores: Set

The category Set has the groupoid Bij as its core, or maximal subcategory which is still a groupoid. As with all cores, Bij is an (essentially) wide subcategory of Set.

There is a functor from categories to groupoids:

Core : Cat → Grpd

And it sends Set to Bij:

Core : Set ↦ Bij

Core(Set) ≅ Bij

cores: Set

This data as json

groupoid	category
Bij	Set