# User talk:Ulf Rehmann

## Another spammer

Please notify me about spammers by dropping a note here with a link to the spammed page:

Template:MSC needs a fix; see here. Boris Tsirelson (talk) 07:57, 13 December 2015 (CET)

An algebraist is needed: Talk:Elementary matrix. Boris Tsirelson (talk) 17:11, 21 March 2015 (CET)

Please look: new (signed) comments are unwelcome? Boris Tsirelson (talk) 20:24, 7 December 2014 (CET)

"Asymptote" does not work anymore! Quite a pity. Boris Tsirelson (talk) 23:09, 17 October 2014 (CEST)

I have notified the sys admin about that. --Ulf Rehmann 00:26, 18 October 2014 (CEST)
It seems to be working again now. --Ulf Rehmann 00:06, 5 November 2014 (CET)

This question is for you. Boris Tsirelson (talk) 20:16, 12 April 2014 (CEST)

Interesting? Boris Tsirelson (talk) 20:55, 5 October 2013 (CEST)

Certainly interesting. In fact, a year ago or so I have tried to follow that way (InftyReader, Abbyy Finereader OCR) as described here to texnify our old image based pages, however, Abbyy OCR was not able to recognize reliably our bad quality images, so InftyReader could not be employed. --Ulf Rehmann 20:14, 12 October 2013 (CEST)

Mathematicians on WP are thinking about EoM: here. --Boris Tsirelson (talk) 16:36, 20 August 2013 (CEST)

Thanks, I have commented there. --Ulf Rehmann 23:17, 20 August 2013 (CEST)

And again: here. Boris Tsirelson (talk) 19:42, 20 August 2014 (CEST)

Talk:EoM:This_project#Another MathJax problem --Boris Tsirelson (talk) 18:37, 1 August 2013 (CEST) Still not fixed. --Boris Tsirelson (talk) 19:53, 13 August 2013 (CEST)

I have again notified the admins. --Ulf Rehmann 22:40, 13 August 2013 (CEST)

## Obsolete pages

Please delete (include pages here for deletion, give a reason for deletion, and make sure no other main pages are linking to those pages by checking "What links here" in "Toolbox"):

User talk:******** ***-***-**** customer phone number ******** help support number (blanked spam; its name is itself spam). Boris Tsirelson (talk) 16:58, 3 February 2016 (CET)

Done --Ulf Rehmann (talk) 17:24, 3 February 2016 (CET)
No, sorry, the redirect page (with the spam name) still exists. Boris Tsirelson (talk) 18:20, 3 February 2016 (CET)
Oops! But now -- I hope. Thanks, Boris. --Ulf Rehmann (talk) 19:43, 3 February 2016 (CET)
Nice. Regretfully, I repeatedly forget that my "move" is futile: I am able to create a new name, but unable to delete the old name. Boris Tsirelson (talk) 20:15, 3 February 2016 (CET)

I inadvertently created the page "Product topology" (in quotes). Could it be deleted, please? Richard Pinch (talk) 16:48, 3 January 2016 (CET)

Done. --Ulf Rehmann (talk) 22:07, 3 January 2016 (CET)

I inadvertently created "discrete direct product" (in quotes) rather than discrete direct product. Could that be deleted please? Richard Pinch (talk) 19:02, 22 November 2014 (CET)

Done. Ulf Rehmann 00:52, 2 June 2013 (CEST)

Can anyone please give a reason for this request? --Ulf Rehmann 23:35, 14 August 2012 (CEST)
See Talk:EoM:This project#Arc simple arc Jordan arc. --Boris Tsirelson 07:16, 15 August 2012 (CEST)
Thanks, Boris. Page Solenoid was still pointing to Arc simple arc Jordan arc, I fixed this. Pages are deleted now. --Ulf Rehmann 10:32, 15 August 2012 (CEST)
Done. --Ulf Rehmann 23:35, 14 August 2012 (CEST)

## Could we also have such a meeting place?

Something similar to this would be useful. (Or like this. But please, not like this.) And by the way, did you see this topic? An EoM-relevant quote from there follows. --Boris Tsirelson 15:05, 13 December 2011 (CET)

"I am the product manager at Springer responsible for managing the technical implementation of the new EOM wiki. I have adapted the citation template documentation for the template:SpringerEOM to use the proper naming convention for the new site. I will be closely watching the site's incoming traffic from WP and updating the ids of WP citations that used the template so that their link-outs will resolve to not only the correct article in the new EOM wiki, but to the version of the article that is identical to the version previously hosted at eom.springer.de.--Nbrothers (talk) 16:13, 30 November 2011 (UTC)"

## Categories

Something is wrong, I guess; we have now both Category:Dynamical Systems and Ordinary Differential Equation and Category:Dynamical Systems and Ordinary Differential Equations. :-)

Thanks. I guess I fixed this.--Ulf Rehmann 22:43, 9 January 2012 (CET)

And by the way: when all first chars are uppercase and when they are not? --Boris Tsirelson 22:23, 9 January 2012 (CET)

Aha, I was careless here. What is the Wikipedia convention? What happens if I rename a category? Will the renameing shift all the entries in its files?--Ulf Rehmann 22:43, 9 January 2012 (CET)
On WP they are generally lowercase; example. No, I am afraid changes in all pages need to be made by hand. And by the way, also replacement of "unofficial" templates to "official" ones (when ready) will be made by hand. Unless we'll create corresponding bots, which is feasible but not so easy (as any programming). --Boris Tsirelson 22:47, 9 January 2012 (CET)
Ok. I'l fix the cases issues. Concerning the templates we'll see later. I guess when programming bots one needs admin access to the machine where the wikimedia is installed? That I don't have (otherwise we'd already have the ParserFunctions ext.... --Ulf Rehmann 23:32, 9 January 2012 (CET)
You mean, the root access. No. Not even admin rights on the wiki. I did it once on Wikipedia, being just a plain user. --Boris Tsirelson 06:47, 10 January 2012 (CET)
But for organizational reasons bots are best run from separate "bot" accounts. This link may be helpful. --Peter Schmitt 15:16, 10 January 2012 (CET)
Thanks for your hints. I did find perl based bot which works.--Ulf Rehmann 12:25, 11 January 2012 (CET)

## Keeping spammers away

It could help, to provide an account only after asking a math question and getting the right answer. The question should be replaced from time to time. Here is one, for example. :-)

Calculate the area of the set of points $(x,y)\in\R^2$ satisfying $\Big( \frac{x-5}{\sqrt{15}-2} \Big)^2 + \Big( \frac{y+3}{\sqrt{15}+2} \Big)^2 \le \frac3\pi \, .$ --Boris Tsirelson 11:12, 14 January 2012 (CET)

And we should not underestimate the problem. See e.g. [1], [2]. --Boris Tsirelson 13:27, 14 January 2012 (CET)

Something like the above has been implemented. Look at Special:Version, search for "ConfirmEdit". Questions are less sophisticated though. --Ulf Rehmann 13:35, 1 February 2012 (CET)
Well, I am glad it is considered seriously. But now (a) it asks me a question whenever I edit something, and (b) a bot can solve such questions easily. I'd prefer not to bother users that have accounts, but to ask harder questions when creating accounts. Like QuestyCaptcha. Of course, it is reasonable to reconsider accounts that exist when such system starts. --Boris Tsirelson 20:51, 3 February 2012 (CET)
I agree with your suggestions: it is inconvenient to have to answer a question every time one does a tiny edit. (In fact I was not aware of this fact until now.) I will mention this to the sysadmins and propose to modify this. However, all these things apparently need time. --Ulf Rehmann 21:24, 3 February 2012 (CET)

Unfortunately, my prediction seems to come true: "Typical solutions tend to be broken by newer spambots". --Boris Tsirelson 10:38, 28 March 2012 (CEST)

And again... --Boris Tsirelson 11:10, 10 May 2012 (CEST)

No, I am not glad but unhappy; it is not considered seriously. Talk:EoM:This project#Spam: what happens? :-( --Boris Tsirelson 21:24, 18 May 2012 (CEST)

Yes, I do understand your feelings, but I hope we can cope with this challenge as well, see here for my response. --Ulf Rehmann 00:07, 19 May 2012 (CEST)

## Suggested move

I suggest to move Surjection to surjective function (leaving a redirect). I think that the adjective is more often used than the noun. (Move is listed among the "user" rights, but there is no "move" button.) --Peter Schmitt 02:47, 14 February 2012 (CET)

I have a "move" button, thus I guess you have, too. But maybe it does not fit into the (not so wide) window. Maybe after "Read", "Edit" and "View history" you have a small black triangle; put the cursor on it, and hopefully you get "Move" and "Watch". --Boris Tsirelson 07:13, 14 February 2012 (CET)
(Blushing) I overlooked this. In fact, now I remember that I noticed it some time ago but did not think of it now ... --Peter Schmitt 17:36, 14 February 2012 (CET)

I propose not to move "surjection" to "surjective function", as there are the notions of "surjective mapping" or "surjective morphism" etc. as well, which are all covered by the notion "surjection". You may want to look into MathSciNet for occurences of "surjection" under "anywhere" or even under "title" to find that notion used quite commonly. --Ulf Rehmann 09:44, 14 February 2012 (CET)

On the contrary, I'd say. In my view, these related concepts are an argument for having pages for each of them and using "surjection" or/and "surjective" as disambiguation pages pointing to them. (By the way, I think that function and mapping need to be better "coordinated". What do you think?) --Peter Schmitt 17:36, 14 February 2012 (CET)
Oh, well, is there any need to split some page of almost empty content (about surjection) into several disambiguated pages? On the other hand, your suggestion to coordinate the pages function, mapping definitely makes sense. But there are much more pages involved, at least Multi-valued mapping, Correspondence (here the notion within algebraic geometry certainly has to be expanded into a complete section, if not into a page of its own), further: Permutation, Morphism, Isomorphism, Epimorphism, Monomorphism, Endomorphism and the like (at the end of Morphism there are more), and then you are in the endless realm of categories, which gives you even more. --Ulf Rehmann 18:36, 14 February 2012 (CET)
I have just operated the page Isomorphism. See there for Categorization and literature, which is may be of relevance for the item Bijection. Mutual links probably were nice. --Ulf Rehmann 14:54, 18 February 2012 (CET)

## Mistake needs correction

By mistake I moved Helly number instead of Helly theorem to Helly's theorem. I could revert the move, but now the redirect has to be deleted. Sorry for that! --Peter Schmitt 23:53, 6 March 2012 (CET)

Done. --Ulf Rehmann 00:13, 7 March 2012 (CET)
Thanks. --Peter Schmitt 00:38, 7 March 2012 (CET)

## Pretex request

Hi Ulf -- I find myself with a bit more time to contribute. Could you do the same "PreTeX"ing for me for Topological algebra, Banach space, Commutative Banach algebra, C*-algebra, Group algebra. I see that this is done by an emacs script, but unfortunately I've not been able to get "its just text" to work on my version of firefox. (if there is another way please let me know/point me to the relevant page). --Jjg 15:52, 16 April 2012 (CEST)

Hi Sergei, it seems you did use a wrong signature: The name of your user page is User:Yakovenko, not what is shown in your signature. But the way, in case you want to change that name, I could do that for you.
Concerning "It's all text": In case you use emacs: You have to give the emacs command "M-x server-start" before clicking on the little edit button in oder to get it to work. I personally don't use firefox, but rather chromium, for which a similar macro has to be applied. The emacs script is very helpful, because allows to use the emacs minibuffer to reedit code which had been keyed in a bit before (just by using the up/down arrows).
Concerning PreTex: Will do so. I'll put the stuff into the respective discussion page of either page, with a short preamble or so. In fact we could do this for every page, since this can be automated. (However, I think the method above allows to work much faster...) --Ulf Rehmann 17:31, 16 April 2012 (CEST)
Hi Ulf -- Actually the sig is right: I am "J.J. Green"!. Thanks for the emacs advice, but in fact the problem seems to be my version of firefox conflicting with addon (there is no "edit button"), I'll try chrome ... Cheers --Jjg 17:41, 16 April 2012 (CEST)
Ok, sorry, I realized too late I was talking to the wrong addressee... Seems I'm talking to too many at the same time. Maybe you put some id into your user page?
The toy for chrome is "Edit with Emacs": https://chrome.google.com/webstore/detail/ljobjlafonikaiipfkggjbhkghgicgoh
You should configure your emacs so that it honors utf-8, and also, that you don't close or leave chrome's edit window while you are editing in emacs, since this would mean you loose contact with the server, and if you close your emacs buffer than its content may be lost.
Another thing: I have, in my .emacs file, a line
because otherwise emacs tends to autofill the whole buffer, thereby destroying WP links. For convenient editing you can use M-x longlines-mode. --Ulf Rehmann 18:20, 16 April 2012 (CEST)
Hi Jim, I have prepared the pretex of the pages you mentioned in their respective talk pages. The Topological algebra had so little tex that I finished that rightaway (except that some MR/ZBL entries are too many, cold you please check and remove the nnosense?).
One more hint: The tex code entries in the above pretex files look like this "". This is good for direct editing. The emacs macro won't work well for that. If you want to use that, you should make a global replacement '' ==> '$_$' first. Then you can apply the macro, and it will traverse you trough all the tex places. --Ulf Rehmann 20:07, 16 April 2012 (CEST)

## Help on sandbox

Do our help pages mention the idea of a (private) sandbox? This would be helpful, see for instance Talk:Normal form and User:Yakovenko/sandbox1. --Boris Tsirelson 07:43, 20 April 2012 (CEST)

I was absolutely thrilled by the simplicity and elegance of this solution! ;-) As a novice to Wiki, I also would suggest one-line help on how to create new pages and rename the old ones (with appropriate caveats about redirection). Sergei Yakovenko 12:44, 20 April 2012 (CEST)

## Help on equation numbering

This also would be helpful; see Talk:EoM:This project#Hadamard theorem. --Boris Tsirelson 16:25, 21 April 2012 (CEST)

## Pages that need some improvement

Hi Ulf. Is there a way to mark a page that needs to be updated or improved (or even created)? Or maybe to add it to a list somewhere? I've been doing some TeX conversion on two pages, and they both need a lot more than simple TeX conversion. They need to be updated and improved. Unfortunately, I have no time to do this right away, but maybe other people have. --Baptiste Calmes 22:41, 23 April 2012 (CEST)

We have to arrange something like a category "deficient". I'll do this within the next days, as there are several such pages which need modification, correction or urgent update. I think a category like this should work, assuming that if a page is deemed by someone to be 'deficient', reasons should be given on the associated talk page. --Ulf Rehmann 23:36, 23 April 2012 (CEST)

## Keywords

Recently I realized that in many cases the terminology is manifold and, say, "fibre bundle" is almost completely synonymous with the "fibration"... Of course, redirects solve the problem, but may be it makes sense to create genuine "keywords" as, say, a template (rather than just a search term) which would be treated almost as the page name when searched for?

How to implement it? By changing the mediawiki software? Much too much for our busy Springer programmers. And yes, redirects solve the problem, and are treated as the page name when searched for. So, is there still a problem? --Boris Tsirelson 11:08, 10 May 2012 (CEST)
I don't know. The problem with redirects is as follows: the same keyword may appear on many pages, while the redirect can be only to one place. I now realize that instead of keywords one could use (sub)categories, but then the question would be again in the numbers, - how strongly branching trees of the form {Differential Geometry -> Bundles and fibrations -> connections -> characteristic classes} we could tolerate. -- Sergei Yakovenko 13:23, 10 May 2012 (CEST)
Then maybe a keyword should be the name of a disambiguation page?
But all that could be discussed rather on Talk:EoM:This project. --Boris Tsirelson 14:42, 10 May 2012 (CEST)

Another example: currently the pages dedicated to connections on vector bundles and connections on a manifold are a complete mess, with two pages on parallel displacement, parallel displacement(2) (which is itself a bad translation from Russian, the right terms should be "translation" or "parallel transport"). I would suggest keeping two closely interlinked pages on "Parallel transport" and "Connection on a bundle", but clearly indicating all other relevant keywords at the beginning. -- Sergei Yakovenko 08:45, 10 May 2012 (CEST)

## Deleting/renaming pages

Hi Ulf. I made a mistake and created a page under the entry Riesz reprensetation theorem. I canceled the content and transported it on a page with the correct title Riesz representation theorem because I did not find a way to rename the wrong one. How can we do that (if possible at all)? Please, could you also remove the page with the misspelled name? Thanks and sorry to bother. Camillo 15:40, 21 July 2012 (CEST)

Hi Camillo: I deleted that page. I think you could just have used "move" in order to give the page a new name. This would cause a redirect from the old page, but is probably less trouble for you. --Ulf Rehmann 16:14, 21 July 2012 (CEST)
Yes, Camillo, pages can be "moved", see the upper-right corner of the menu (triangle to the right of "View history"). --Boris Tsirelson 18:18, 21 July 2012 (CEST)
Ah, tricky that tiny triangle! Sorry, I guess it must be written somewhere, but I have the bad tendency of learning things by trial and error...Camillo 18:43, 21 July 2012 (CEST)

## Adding MSC and Zbl references

Hello Ulf. I have been making quite a lot of changes... before a question came to my mind. So far I have been adding MSC and Zbl links one by one myself: is that the only way or is there a faster method I am unaware of? Camillo 17:48, 9 September 2012 (CEST)

Hi Camillo: Yes, there is some. I have a perl script which automatically tries to find and insert the MR/ZBL links. I have just done this for the page Absolute_summability from your user page, to give you an idea. I could do this for all pages mentioned there, by applying some batch job. I already did this, e.g., for the pages mentioned on my user page, see User:Ulf_Rehmann/pages_related_to_algebraic_groups. However, the script does make mistakes. It won't find everything, and it also may find too many, e.g., if a reference does contain mistakes. Let me know if you want to give it a try. --Ulf Rehmann 22:17, 10 September 2012 (CEST)
Hello Ulf! It would be very helpful to apply your batch job to all the pages which I mention in User:Camillo.delellis as pages which I will modify sooner later. But among the ones which I already modified, it makes sense to do it only in

To the others I already added all the MSC and Zbl myself. Thanks a lot. Camillo (talk) 21:32, 15 September 2012 (CEST)

## EoM and Windows

Ulf, to your attention.--Boris Tsirelson (talk) 14:57, 25 October 2012 (CEST)

## Issue on the "divisor" page

The page for divisor makes a (suspect) definition of a Cartier divisor on a general ringed space. It does this in the expected way by looking at global sections of a particular quotient of the sheaf of meromorphic functions, so I wanted to point out to you that it's not possible to define the sheaf of meromorphic functions on a general ringed space (at least not in the way you described, which would have been my guess, or in any other way that I know of)!

The problem is that total-quotient-ring isn't a functor: a homomorphism of rings only gives rise to one of total quotient rings only if the kernel consists entirely of zerodivisors, which needn't be the case for a general ringed space. (For arbitrary schemes, this is indeed the case, since a nonzerodivisor will remain nonzero in every open subset.) There may be a different way to construct Cartier divisors on ringed spaces, but I believe that what's currently written is incorrect! Xander Flood (talk) 03:45, 3 June 2014 (CEST)

Thanks for pointing this out. I have added a link to this in the comment page of Divisor_(algebraic_geometry) and will try to get this straightened out soon (as time permits). --Ulf Rehmann 00:46, 5 November 2014 (CET)

For several weeks now I have found myself unable to add external links, such as MSC categories, ZBL, MR, DOI references, or add new pages (even redirects). The issue seem to be the demise of the cats-and-dogs "captcha" facility. This is making it hard to contribute effectively. In the absence of even a temporary fix, perhaps you might like to consider granting sufficiently advanced permissions, on a temporary basis, of course, to regular users to enable them to do these things? Richard Pinch (talk) 17:57, 16 November 2014 (CET)

Yes, the situation is very unpleasant for many. I have a long nagging correspondence with the admins, the last message (dated Nov 13) says The new captcha is being installed in our development environment. Will keep you posted. I think I personally cannot grant those rights -- otherwise I would have done this already. Hopefully next week the new captcha will be installed. --Ulf Rehmann 18:48, 16 November 2014 (CET)
Thanks for that. I'll wait until the site is fully functioning again. Perhaps you would be so kind as to post on my talk page when that happens, please? That should alert me by email. Richard Pinch (talk) 19:13, 16 November 2014 (CET)
This seems to be resolved. A new captcha is installed. --Ulf Rehmann 18:57, 19 November 2014 (CET)
There still seem to be multiple bogus new user accounts and spam pages. Do you wish to extend the ability to delete pages and block spammers to a few more trusted users? Richard Pinch (talk) 19:31, 22 November 2014 (CET)
Ulf is an administrator, not a bureaucrat; he cannot. Boris Tsirelson (talk) 21:07, 22 November 2014 (CET)
Then perhaps he might wish to pass the suggestion on to someone who can act on it. Mind you, it's only a suggestion, on the assumption that help in getting rid of this nonsense would be welcome. Richard Pinch (talk) 21:36, 22 November 2014 (CET)
THanks a lot, that is very kind
Are you interested in helping? I should warn you: The mass deleting/blocking toys here are pretty uncomfortable (beta stuff). I do need the help of some perl scripts and the like in order to manage them. Anyway, I have asked for employing more admins. Ulf Rehmann 12:06, 24 November 2014 (CET)
We now have new and hopefully more efficient captcha questions installed. Let's see how the spam bots will cope with them! --Ulf Rehmann 18:33, 25 November 2014 (CET)
I would be happy to help out if you wish. Richard Pinch (talk) 21:52, 26 November 2014 (CET)
Thanks a lot, that is very kind of you. I already asked, but at the moment it seems the bureaucrats are hesitating to enlarge the group of administrators. See here for these groups. --Ulf Rehmann 22:28, 26 November 2014 (CET)
How to Cite This Entry:
Ulf Rehmann. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Ulf_Rehmann&oldid=37704