Questions tagged [locales]

Questions taking place in the category of locales, which is given by the opposite of the category of frames. Also appropriate for questions about pointless topology.

19 questions with no upvoted or accepted answers
Filter by
Sorted by
Tagged with
25 votes
0 answers
1k views

$\infty$-topos and localic $\infty$-groupoids?

It's known that every classical (Grothendieck) topos is equivalent to the topos of sheaves on a localic groupoid (a groupoid in the category of locales). For the record, this is proved by, starting ...
Simon Henry's user avatar
  • 39.9k
12 votes
0 answers
406 views

What does the localic reflection of a classifying topos classify?

Let $\mathbb{T}$ be a geometric theory. Let $\mathrm{Set}[\mathbb{T}]$ be its classifying topos, such that geometric morphisms from any (cocomplete) topos $\mathcal{E}$ into $\mathrm{Set}[\mathbb{T}]$ ...
Ingo Blechschmidt's user avatar
8 votes
0 answers
102 views

Locales satisfying DC?

Is there a nice (topological) characterization of the locales such that the axiom of dependant choices holds in the internal logic of the topos of sheaves ? I would also be interested in the case of ...
Simon Henry's user avatar
  • 39.9k
6 votes
0 answers
146 views

Spatiality of products of locally compact locales

In Johnstone´s Sketches of an Elephant Volume 2, page 716, lemma 4.1.8 states that for spatial locales $X$ and $Y$ with $X$ locally compact then the locale product $X\times Y$ is spatial. Is this ...
Angel Zaldívar's user avatar
6 votes
0 answers
251 views

Are regular epi of locale stably epic?

It is well know that the category of locales is not a regular category, that is the pullback of a regular epimorphism is not always a regular epimorphism: for example, the classical counterexample ...
Simon Henry's user avatar
  • 39.9k
5 votes
0 answers
162 views

Within pointless topology inside of choiceless constructivism, prove that division is possible

In Frank Waaldijk's paper on the foundations of constructive analysis, Waaldijk shows that various definitions of "continuous function" for functions of the form $f: \mathbb R \to \mathbb R$ ...
wlad's user avatar
  • 4,823
5 votes
0 answers
250 views

Uniqueness of localic analogue of Radon-Nikodym derivatives

In classical probability theory, Radon-Nikodym derivatives are unique up to measure-0 sets of the background measure. I am wondering whether the following statement, intended to state an analogue of ...
Ben's user avatar
  • 293
5 votes
0 answers
384 views

Inductive generation of non-spatial locales

Is there an example of a locale/formal space which is not spatial (i.e., one can prove it is not spatial, rather than something like $\mathbb{R}$, where spatiality is independent in a constructive ...
Ben's user avatar
  • 293
4 votes
0 answers
240 views

Is this property of continuous maps equivalent to some more familiar condition?

Let $f : X \rightarrow Y$ be a continuous map. Suppose that, for each collection of open sets $\{ V_i \}_{i \in I}\subset X $, $$ \bigcup_{U \subset Y \text{ open}, \ f^{-1}(U) \subset \bigcup_{i \in ...
Ronald J. Zallman's user avatar
4 votes
0 answers
102 views

Compact subspace of sober space

We know from lemma 1.2.5 in part C of Sketches of an Elephant (by Johnstone) that both open and closed subspaces of a sober space are again sober. This raises the following question. Question: Is a ...
Math Student 020's user avatar
3 votes
0 answers
425 views

Topos Theory, internal Heyting Algebra

Given a topos $\mathcal{E}$ with subobject classifier $\Omega$. If we denote by $N\Omega$ the former of all local operators on $\Omega$, that is, Lawvere–Tierney topologies of $\mathcal{E}$, it is ...
Angel Zaldívar's user avatar
3 votes
0 answers
223 views

pullback of a morphism of locale which is an isomorphism?

Let $A,B$ be two locales over a locale $X$, and $f:A\rightarrow B$ a morphism of locale over $X$. Let also $g:X'\rightarrow X$ be a surjection of locale such that the pullback of $f$ along $g$ is an ...
Simon Henry's user avatar
  • 39.9k
2 votes
0 answers
70 views

What is known about sublocales defined by regular nuclei?

(For basic terminology, which is supposed to be standard anyway, see this other question, which inspired this one.) I am interested in nuclei $j\colon L\to L$ on a frame $L$ which are regular elements ...
Gro-Tsen's user avatar
  • 29.8k
2 votes
0 answers
158 views

Concrete description of “DeMorganian” open sets

Let me begin with a few definitions. My question will be basically how to simplify them to something more manageable. The motivation for these definitions is given at the end. Let $X$ be a ...
Gro-Tsen's user avatar
  • 29.8k
2 votes
0 answers
96 views

Concrete topological objects and notions in the category of locales

I have read Peter Johnstone's “The Point of Pointless Topology” and the idea that topological spaces are not quite the right abstraction for topology seems, at least philosophically, rather appealing. ...
user1892304's user avatar
2 votes
0 answers
111 views

Explicit description of the canonical $\pi_G: \mathrm{Sh}(G_0)\to B_S(\mathbf{G})$

Given a localic groupoid $\mathbf{G} = (G_1\overset{d_0}{\underset{d_1}{\rightrightarrows}}G_0)$ and letting $B\mathbf{G}$ denote its classifying topos, I'm looking for a explicit description of the ...
BlackBoxedConchqueror's user avatar
2 votes
0 answers
155 views

surjection of localic infinity toposes?

Hello! Is there a simple 'topological' condition to detect whenever a morphism of locales $f : X \rightarrow Y$ induces a surjection of infinity-toposes $f : \mathrm{Sh}_{\infty}(X) \rightarrow \...
Simon Henry's user avatar
  • 39.9k
0 votes
0 answers
117 views

Colimits in the category of suplattices

I want to compute coequalizers in the category $\mathcal{S}up$ of complete lattices and $\bigvee$-preserving maps. One way (I think?) is to use the dual equivalence $$ \mathcal{Sup} \leftrightarrows \...
Hans's user avatar
  • 137
0 votes
0 answers
229 views

Is there a translation invariant measure on an infinite dimensional space 'without points'?

This is just a reference request. I thought I'd come across a paper demonstrating that there is a translation invariant measure on an infinite-dimensional space without 'points' whilst browsing the ...
Mozibur Ullah's user avatar