Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

This looks pretty obvious, but an endofunctor $F : Set \to Set$ seems to be a presheaf over $Set^{op}$.

Is there any useful fact that can be learnt from this view of endofunctors?

share|cite|improve this question
2  
We usually only consider presheaves over small categories. $\mathbf{Set}$ is not small. – Zhen Lin Nov 22 '13 at 16:09
1  
Perhaps one should restrict to $F$ preserving directed colimits, or equivalently to functors $F : \mathsf{FinSet} \to \mathsf{Set}$. This is related to combinatorial species. – Martin Brandenburg Nov 23 '13 at 0:22

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.