Talk:Pointless topology

Joke

There's got to be a good joke or two about this title... --LDC

Thats why I added /Talk, but I bottled it... How about "Isn't the title a tortology"

(I think that's "tautology") :)

Only if it has something to do with pie.

If the topology is so pointless, why is anyone studying it? — JIP | Talk 06:50, 25 August 2005 (UTC)

The title should of course be renamed. // Jens Persson (193.10.114.85 (talk) 13:49, 10 January 2008 (UTC))

Yeah, I thought people referred to it as "point-free" topology.. —Preceding unsigned comment added by 68.38.205.29 (talk) 15:06, 1 September 2009 (UTC)

1) the people using the term "pointless spaces" used it of course because they were well aware of all possible meanings - I prefer 'locale theory'

2) I never understood why we needed yet another term. "pointfree topology" sounds just odd to me. —Preceding unsigned comment added by 114.182.153.194 (talk) 15:46, 20 October 2009 (UTC)

Weasel words and open questions

In my opinion, the article as it stands now contains too many weasel words and cliffhangers:

Some proponents claim that this new category has certain natural properties which make it preferable.

Who claims this, and what are those certain natural properties?

The concept of "product of locales" diverges slightly from the concept of "product of topological spaces", and this divergence has been called a disadvantage of the locale approach. Others claim that the locale product is more natural and point to several of its "desirable" properties which are not shared by products of topological spaces.

In which way do the concepts "product of locales" and "product of topological spaces" diverge? Who calls this divergence a disadvantage of the locale approach and why? What are those "desirable" properties which are not shared by products of topological spaces? Does this all mean that the concept of pointless topology is controversially discussed amongst experts? When were these ideas introduced and by whom? Inquiring minds want to know. :-) -- Tobias Bergemann 06:18, 25 August 2005 (UTC)

Hi. I am Eric Zenk. I am a mathematician who studies pointless topology. Hopefully reading the following few sentences will enlighten somewhat. (webpage avialable: http://sitemason.vanderbilt.edu/page/deeHFS)

Regarding products of locales vs products of spaces. Products of topological spaces are easier to compute; the underlying set of a product Product(X_i) space is the set theoretic product, and the topology is the finest making all projections continuous.

The locale product (i.e., frame coproduct) is an infinitary algebraic object. Its frame of open parts is generated by all functions (U_i) where each U_i is open in X_i and all but finitely many U_i are equal to their respective X_i. The relations needed are those which guarantee the coprojections O(X_i)--> O(Product X_i) are continuous. See Peter Johnstone's Book _Stone Spaces_ for more details. The difficulty with this approach is that it is somewhat difficult to compute with the frame generated in this manner. (cf. difficulties figuring out which group is presented by a given set of generators and relations, then multiply by the fact that infinitary operations, i.e. joins, are involved)

As for differences: products of paracompact spaces needn't be paracompact (or even normal). On the contrary: products of paracompact locales are paracompact. Other differences between locales and spaces: each locale has a smallest dense sublocale, while most spaces do not.

To read more about locales vs spaces: check for papers/authors mentioned below. 1. John Isbell, Atomless Parts of Spaces, Published in Math. Scand., something like 1974 (Isbell is difficult to read, but seems brillant to me. He is first to notice differences between locales and spaces and to exploit the advantages of locales.)

2. Till Plewe was a doctoral student of Isbell. His published work is closer to the view point of Isbell than any other author [true, for obvious reasons, but also by choice TP]

3. Bernard Banaschewski, Peter Johnstone, James Madden, Ales Pultr, Joanne Walters-Wayland, Richard Ball, Andrew Molitor, Marcel Erne, Harold Simmons, Dona Papert, Dowker (cannot recall first name)[Hugh (TP)], Vermeer, Martin Escardo, Jorge Martinez (was my dissertation advisor), Steven Vickers are among the people who have published in the area.

Madden, Martinez, Ball and I are interested in connections between frames and lattice ordered-groups.

Simmons has published a lot about the congruence lattice of a frame, which actually turns out to be another frame, with each frame embedding in the frame of congruences on it; moreover the congruence lattice of a frame is generated by freely adding a complement to each open part. Topologically, this construction resembles the continuous map from the (discrete version of) the underlying set of a topological space, to the topological space. Unlike in point set topology, this process (giving each open part a complement) does not necessarily result in a discrete space after one iteration. There are frames for which one can iteratively add complements, and repeat ad infinitum without ever obtaining a Boolean frame.

Walters-Wayland has written mostly on uniform structures on a frame. (analogous to uniform spaces.)

— Preceding unsigned comment added by 208.182.75.11 (talk) 00:18, 9 September 2005

I am Till Plewe. John Isbell's papers certainly have a very high density of interesting ideas. The downside being of course that they are harder to read => less people try to understand them => the papers are less influential then they ought to be.

Bernard Banaschewski, Peter Johnstone, James Madden, Ales Pultr, Joanne Walters-Wayland, Richard Ball, Andrew Molitor, Marcel Erne, Harold Simmons, Dona Papert, Dowker (cannot recall first name)

Hugh

Simmons has published a lot about the congruence lattice of a frame, which actually turns out to be another frame, with each frame embedding in the frame of congruences on it; moreover the congruence lattice of a frame is generated by freely adding a complement to each open part. Topologically, this construction resembles the continuous map from the (discrete version of) the underlying set of a topological space, to the topological space. Unlike in point set topology, this process (giving each open part a complement) does not necessarily result in a discrete space after one iteration. There are frames for which one can iteratively add complements, and repeat ad infinitum without ever obtaining a Boolean frame.

One of my papers has some further results on how late this process can stop but nothing impressive

— Preceding unsigned comment added by 114.182.153.194 (talk) 15:56, 20 October 2009

The original comment above was added by Eric Zenk from IP 208.182.75.11, but was subsequently modified by an editor from 66.4.125.11 a few minutes later. Plewe added his comments in square brackets. I have moved Plewe's comments out of Zenk's, and added quotations to indicate which part of Zenk's comments Plewe was replying to. --Joshua Issac (talk) 22:05, 27 December 2014 (UTC)

Overlap with other articles

There is some overlap between this article and complete Heyting algebra and Stone duality that could/should be refactored. -- Tobias Bergemann 07:08, 25 August 2005 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Pointless topology/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

The second half of the section "Relation to point-set topology" seems to be a copy of part of the introduction of one of my (Till Plewe) papers (probably sublocale lattices). I think the topic would deserve a slightly more balanced treatment. Comparison with point set topology provides a starting point for a discussion of locale theory but should not be the main point.

Last edited at 16:06, 20 October 2009 (UTC). Substituted at 02:29, 5 May 2016 (UTC)

Written like an abstract not a wiki page

For example, "Regarding the advantages of the point-free approach let us point out, for example, the fact that..."

72.136.16.173 (talk) 05:54, 15 April 2020 (UTC)