Category of elements
From Wikipedia, the free encyclopedia
In category theory, for every presheaf 
the category of elements 
of P is the category defined as follows:
- its objects are pairs (A,a) where A is an object of C and
, - its morphisms
are the morphisms 
of C such that a = P(f)(b).
This construction can be extended into a functor 
from 
to 
, the category of small categories.
