4
$\begingroup$

Let $Topos$ be the $(2,1)$-category of Grothendieck toposes and geometric morphisms. This is a $V$-sized, locally $V$-sized, locally locally small $(2,1)$-category with all small (2,1)-colimits (=pseudocolimits) and terminal object given by the topos $Set$.

Question 1: Is $Set$ a tiny object of $Topos$?

That is, does the covariant hom-functor $Pts = Topos(Set,-): Topos \to GPD$ preserve all small (2,1)-colimits?

Question 2: If so, what are some other tiny objects in $Topos$? If not, are there any at all?

This question was inspired by thinking about this fundamental question of Jonathan Sterling.

I'd also be interested in the $\infty$-categorical versions of these questions.

I'm pretty sure that $Topos(Set,-)$ commutes with small coproducts. So it would suffice to consider pseudocoequalizers or pseudopushouts.

As a De Morgan topos, Theorem D4.6.15 of the Elephant shows that $Set$ is projective with respect to proper separated localic surjections. But I'm not sure how those compare to descent morphisms, nor how close projectiveness with respect to descent morphisms would come to $Topos(Set,-)$ preserving descent objects.

$\endgroup$
2

1 Answer 1

6
$\begingroup$

The answer to your question is unfortunately no. The terminal topos is not even finitely presentable.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.