4

I've been trying to find some useful categorical facts about the category of schemes, locally ringed spaces and ringed spaces (that I shall denote by $\text{Sch}$, $\text{LRS}$ and $\text{RS}$ respectively). The motivation is that I'm trying to compute some (co)limits explicitly in the category of schemes.

There's this excellent answer here On limits, schemes and Spec functor , but I still have some doubts.

More precisely, I want to know about the following assertions:

1) Is the category of locally ringed spaces (co)complete?

In the answer cited above, the references implies the existence of cofiltered limits and filtered colimits, however as I understand the notion of filtered in these cases is restricted to the case where the index category is a poset.

2)Is the category of ringed spaces (co)complete?

3)What can be said about the underlying topological space of the (co)limit of locally ringed spaces? (Is it the (co)limit of the topological spaces?)

4)What can be said about the underlying topological space of the (co)limit of ringed spaces? (Is it the (co)limit of the topological spaces)

5)What can be said about the underlying topological space of the colimit of schemes? (Is it the (co)limit of the topological spaces)

Obviously, the underlying topological space of the pullback of schemes is not the pullback of the topological spaces (for instance, $\text{Spec} (\mathbb{C}) \times_{\text{Spec} (\mathbb{R})}\text{Spec} (\mathbb{C}) \cong \text{Spec} (\mathbb{C}\times\mathbb{C})$ by $a \otimes z \mapsto (az, a\overline{z})$), but the case of push outs seems to be true.

6) Are (co)limits preserved under the inclusions $\text{Sch} \hookrightarrow\text{LRS} \hookrightarrow \text{RS}$?

7) For each forgetful functor $U : \mathcal{C} \rightarrow \mathcal{D}$, where $\mathcal{C}$ and $\mathcal{D}$ are equal to $\text{Sch}$, $\text{LRS}$ and $\text{RS}$ (for all possible coherent substitutions), are there adjoint functors?

8) For each inclusion $\mathcal{C} \hookrightarrow \mathcal{D}$, where $\mathcal{C}$ and $\mathcal{D}$ are equal to $\text{Sch}$, $\text{LRS}$ and $\text{RS}$ (for all possible coherent substitutions), are there adjoint functors?

According to http://arxiv.org/abs/1103.2139 [Cor. 6], the inclusion $\text{LRS} \hookrightarrow \text{RS}$ have a right adjoint given by localization of the terminal prime system.

Thanks in advance.

user40276
  • 5,543
  • 1
    It is usually considered bad form to ask lots of questions at once. – Zhen Lin Aug 24 '15 at 06:46
  • 1
    @ZhenLin So what do you suggest? I can split this question in more questions, but since they're all related to the same goal I'm not sure how I should split it. – user40276 Aug 25 '15 at 06:42
  • 1
    I agree with Zhen Lin but also think that the questions are quite interesting. I will try to give answers to some of the questions when I have thought about them some more. To answer 6), you might research quotients of schemes. – Ingo Blechschmidt Sep 15 '15 at 21:50
  • 1
    @IngoBlechschmidt My question have already been partially solved here http://mathoverflow.net/questions/216060/about-the-relation-between-the-categories-textsch-textlrs-and-text . I don't know if I should delete this question here (on mathstack)... – user40276 Sep 16 '15 at 05:54

0 Answers0