Definition 4.9.10.  Let u ∈ ℕ. We define:
Ringu := [Ring(Hom(A, B))A,B ∈ Ring(idC)C ∈ Ring(∘)D,E,F ∈ Ring]u is a/an u-small category
Remarks.

The objects of this category are actually isomorphism classes of rings.

References.