nLab
finite category

Finite categories

Definition

A finite category C is a category internal to the category FinSet of finite sets.

This means that a finite category consists of

(Notice that the latter implies the former, since for every object there is the identity morphism on that object).

Similarly, a locally finite category is a category enriched over FinSet, that is a category whose hom-sets are all finite.

(Locally) finite categories may also be called (locally) ω-small; this generalises from ω (the set of natural numbers) to (other) inaccessible cardinals (or, equivalently, Grothendieck universes).

Limits and colimits

One is often interested in whether an arbitrary category D has limits and colimits indexed by finite categories. A category with all finite limits is called finitely complete or left exact (or lex for short). A category with all finite colimits is called finitely cocomplete or right exact.

Revised on June 19, 2013 12:27:01 by Urs Schreiber (82.169.65.155)