Moderator's Note: I am (at least) temporarily closing this thread. New suggestions should be made in the current Winter tag cleanup meta-thread.

This is half a question, half an announcement. I will be going through the list of tags and merging particularly bad ones (e.g. ones that aren't mathematical or are too specific) into the tag [tag-removed]. I will also be creating tag synonyms. Any suggestions for mergers or synonyms should go into this thread.

Roughly speaking, here is my general policy: if I can't imagine a person classifying a tag as either interesting or ignored, I'm getting rid of it.

Edit: This thread and the tag changes archive have been merged for simplicity.

Edit2: I've started a new summary thread. Moderators: please allow sufficient time (at least 1 day) for discussion on "non-trivial" proposals, before actual implementation (some of such "non-trivial" ones are still not yet resolved, see the list below). After implementation please first comment to indicate implementation (to get a date stamp), then delete the answer to unclutter, and add a line to the summary thread.


closed as off-topic by arjafi Feb 6 '14 at 9:08

  • This question does not appear to be about Mathematics Stack Exchange or the software that powers the Stack Exchange network within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

Changes are automatically recorded at , but for changes initiated by moderators please also post them as answers in this thread so that they can be voted and commented upon. In theory, reversal or a different synonym might be a result of the discussion in some cases. (In practice, the moderator judgements have been reasonable as one can see at that link.) – T.. Dec 17 '10 at 5:59
I deleted two tag synonyms experimentally, but unfortunately I do not remember what they are. Anyone who misses them enough to remember them should post it in this thread and let it be voted on. – Qiaochu Yuan Dec 17 '10 at 6:01
@T..: should I also report on the tags I've merged? – Qiaochu Yuan Dec 17 '10 at 6:08
I think it's good practice to document any changes if it's not completely annoying to do so. Maybe a separate "tag changes history" thread can be the archive and this one for the suggestions. This is just my preference, I have no idea what others might think, but because the tag system already contains some evolved structure it seems like any modification should be documented. This might also be useful for other purposes later. – T.. Dec 17 '10 at 6:11
@T..: I'm not so sure. Most of what I'll be doing is essentially garbage-collection and I don't think that's worth documenting. Anything that's not obviously garbage-collection I'll propose in this thread. – Qiaochu Yuan Dec 17 '10 at 6:14
Also, I have the feeling that decisions on tags will often arise after a certain amount of back and forth about competing proposals (see e.g. the current discussion on [cardinals] or the earlier one that led to [elementary-set-theory]) and it is easy to forget the logic of the decision later on. The tag system is part of the knowledge-organization function performed by the site, so it could be very interesting over time to see how the choices are made and what principles can be distilled from the process. – T.. Dec 17 '10 at 6:18
re: garbage collection, individual decisions might be trivial but taken cumulatively there may be non-obvious decisions to be made, patterns noticed or design criteria articulated. It would suffice to have a single "garbage tags" posting (list each removed tag plus number of times it was used) that keeps growing from the garbage collection in progress, but visibility of the changes has its own value. Simply knowing the fraction and nature of junk tags is useful for considering the future evolution of the tag system. – T.. Dec 17 '10 at 6:23
Thanks for the additional thread. May I suggest the format "[original tag], change, number of postings affected, sample link". – T.. Dec 17 '10 at 7:49
@T..: the latter. – Qiaochu Yuan Dec 17 '10 at 8:47
why are people downvoting? also, this is much better idea than the previous one. – Sean Tilson Dec 17 '10 at 15:10
This seems to have gotten absolutely unreadable. I think we'd be much better off with each request in its own question. – Isaac Apr 29 '11 at 18:36
@Qiaochu: Because it takes too long to figure out what's new or changed when this monster-question gets bumped to the top. If one person has many tag changes to suggest, they can post them all in one meta question if they want, but I think we'd be more likely to get useful information from answers on such questions and votes on the question and answers if each suggestion were its own question. – Isaac Apr 30 '11 at 0:20
@Qiaochu ...And comments in new answers are folded immediately (because there are too many comments in total) — I second the idea of starting new thread or something – Grigory M Aug 18 '11 at 12:39
New thread: – Grigory M Jan 16 '14 at 16:08
This question is now superseded by the Winter tag cleanup thread. – arjafi Feb 6 '14 at 9:08

70 Answers 70

Summary Thread for Implemented Changes

(Please do not edit this answer unless you are a moderator. All proposed changes should be added as new answers to the question. Users with 10K+ reputation will still be able to see the original dates of proposals and implementations.)

One should also note that there exists a page on the StackExchange platform specifically listing all tag synonyms and proposals for tag synonyms. Any user with 2.5K+ rep can go and vote up/down proposals for synonyms.

The following is sorted alphabetically by the name of the deprecated tag. Format is "(deprecated tag name) s/m (principal tag name)" in the case of synonyms or mere merging without synonyms; and "(deprecated tag name) d" in the case of removed tag names.

Awesome; thanks for doing this, Willie! – Qiaochu Yuan Jun 24 '11 at 15:23
I do not like the alphabetically ordering. Is it possible to add another answer with chronological log as well? Alphabetical makes it impossible to find with a glance the last merges and whatnot. – Asaf Karagila Jul 6 '11 at 19:36
@Asaf: click on the "edited 4 hours ago" and read the diff. It is more succinct, and has guaranteed correct date/time-stamps. Alphabetical makes it easier for me to check whether a tag that I am suspicious of has been discussed before and deleted before. – Willie Wong Jul 7 '11 at 0:05
@Willie: I know how to get there. I was hoping there could be another answer with a chronological wangdangdoodle of the merges. Do you mind if I add such answer and manage it? – Asaf Karagila Jul 7 '11 at 6:13
@Asaf: sure, go ahead if you'd like to do the work. Thanks, btw, for offering to help! – Willie Wong Jul 7 '11 at 10:56
Apart from merging and removing tags, some tags were "divided" - replaced by two new tags. I know of algebra and lattices, as of this moment. Should changes of this kind be included into the list? – Martin Sleziak Aug 11 '12 at 7:00
On an unrelated note, I've seen an announcement that Willie and Zev are taking break from the moderator duties for some time. (I hope they'll come back later.) So far Willie did all edits to this post. Is some other moderator going to take care of this list? (It explicitly states: Please do not edit this answer unless you are a moderator. I suppose there is some good reason for this; probably other users don't see all changes made by moderators.) – Martin Sleziak Aug 11 '12 at 7:01

Can we please delete ?

This feels like a meta tag.

BTW there is a separate question Tags (proof-strategy) and (proof-writing). Unfortunately with no answers (at the moment). – Martin Sleziak Jun 30 '12 at 12:30

[Edit] Within the last month somebody has created a tag . There are currently 9 questions with this tag. I would propose to synonymize this with . The latter "mother tag" has only 223 questions itself, so I don't see the need to splinter off a handful of questions.

As I don't have a score of +5 in I cannot suggest a synonym at this time. Instead I will reach for the fine-tuning sledgehammer of manually removing this tag. If somebody objects, let me know.

If the tag reappears, I will bring it up again and/or flag a moderator. [/Edit]

During my first 3 weeks here I have encountered a few peculiarities:

The tag has only a single post. I don't know for how long we commonly wait to have meaningful statistical evidence, but it sounds like a merger with is due.

Another thing that I found odd was the tag . Of the 5 posts carrying that tag one was about octonions, the rest were (junior) high school level questions about the role of division in school level algebra. I rather got that the intention of the tag was to collect questions related to division algebras aka skewfields aka division rings, but I may be wrong. The confusion may stem from the fact that this tag has no wiki entry. If it is meant to be part of , then I could write a wiki for it.

Okay, 'golay-code' has been removed (I think it is too specific), the weird 'division-algebra' questions have been retagged. I've renamed 'division-algebra' to 'division-algebras' (note the plural) to be more in accord with our general tendency of using plural forms for objects in the tags. – Willie Wong Jun 24 '11 at 1:00
Thank you for keeping an eye out for these, and I would like to take you up on your offer of writing a tag-wiki for division-algebras (it should be a part of abstract algebra). If you drop me an @-notification when you do that, I'll approve the Wiki proposal ASAP. – Willie Wong Jun 24 '11 at 1:02

Do we really need both the and tags?

If not, could we merge one into the other?

And if so, could someone give a good explanation of the difference between the two?

Edit by J.M.: If we do merge these two, which name do we keep? (A rewrite of the tag blurb and tag wiki might also be in order.)

I think this has to do with this thread by Bill, see also his answer here. – t.b. Oct 24 '11 at 18:31
@t.b.: Thanks. I'm pretty sure I had read that post at some point, but I had forgotten about it. It looks like his suggestion was only partly implemented, though: We now have integration, integral, and definite-integral! Or was integration the choice of name for questions involving indefinite integration? – Mike Spivey Oct 24 '11 at 19:34
At this moment tag info for integral is: Questions on the evaluation of definite and indefinite integrals. For integration: All aspects of integration, including the definition of the integral and computing indefinite integrals (antiderivatives). So it seems to me that integration was intended for "theoretical" question and integral for computations, but they were definitely not used in this way. – Martin Sleziak Nov 27 '11 at 7:25
This was also discussed in a separate question. Obviously, I've forgotten about this post, when I was posting that question. – Martin Sleziak Jun 1 '13 at 4:46
Perhaps it is worth mentioning here that the two tags now are synonyms. – Martin Sleziak Mar 23 '14 at 17:36

I proposed creating as a synonym for in the chat, where it met with some support. Rationale:

  • is about the only commonly used tag which is an abbreviation. Judging from the other tags they see, new users would not expect abbreviations in tags.
  • While "PDE" is a completely standard abbreviation for mathematicians, it is less so for students in service-level courses, who supply a large number of PDE questions.
  • When a user tries to tag their question with (partial-diff...) and finds no match, they are likely to delete "partial" and mistag the question as (differential-equations). This is one of the more common mistags I see.
That said, I could not figure out how tag synonyms are created, so this is left up to the more knowledgeable people. – user53153 Mar 5 '13 at 1:48
If you have "enough" reputation in the particular tag, you can suggest a synonym. – Asaf Karagila Mar 5 '13 at 1:56
Go to the tag page pde, click synonyms, enter "partial-differential-equations" in the Suggest box. – Rahul Mar 5 '13 at 1:58
@RahulNarain Thanks! Now I see why this synonym wasn't created before: the 25 character limit for tags. Grr. // So I tried to suggest partial-differential-eqns which would serve the same purpose: users would see it when beginning to type "partial-di". Failure #2: "the suggested tag must exist in the system before suggesting it as a synonym". – user53153 Mar 5 '13 at 2:47
Well, there are two ways of this, either create the tag by tagging at least one questions by it (the tag can be removed after the synonym had been suggested), or ask a moderator, who can create synonym (without waiting for votes from users to approve the synonym). – Martin Sleziak Mar 5 '13 at 6:25
Okay, done. (That 25 character limit is the original reason why I chose (pde) instead of (partial...). ) – Willie Wong Mar 5 '13 at 11:43

Chronological Summary Thread for Implemented Changes

Taking on Willie's notation, the following is sorted chronologically by the time (newer is higher) of the action taken. Format is "(deprecated tag name) s/m (principal tag name)" in the case of synonyms or mere merging without synonyms; and "(deprecated tag name) d" in the case of removed tag names.

July, 2011

July, 9th

July 7th

July 6th

July 5th

Actions B.C.

Instead of B.C., I think it should be B.A.K.! Thanks! – Willie Wong Jul 8 '11 at 9:02
@Willie: B.C. stands for Before Caring (about it) :-) – Asaf Karagila Jul 8 '11 at 9:15

I think should be merged into and synonymized to .

Hmm... a context free language is generated by context free grammar; I am not exactly sure we want the arrow to go the direction you proposed. Can you explain briefly why the arrow should go one way, and not the other? Thanks! – Willie Wong Feb 21 '13 at 11:23
I agree with you. When I wrote the proposal I was not thinking that the merge was asymmetric. – MJD Feb 21 '13 at 13:54
Okay, I'll do the merge now. – Willie Wong Feb 21 '13 at 13:55

Can we kill the tag? A look at the five questions currently tagged as such already indicates two-and-a-half different meanings for (completeness). That is without considering geodesic completeness in geometry, completeness of logical systems, completeness of vector fields, completeness of measure spaces, completeness of an orthonormal set of vectors in a Hilbert space, completeness for graphs, completeness of partially ordered sets, ... and I am sure there must be others.

Edit: [A.K]: March $10^{\text{th}}$, I have ruthlessly butchered this tag away!

Edit II [A.K]: March $20^{\text{th}}$, I have killed the tag again. Please remove it, and/or point to this post when it comes back to life the next time.

I agree: completeness as a tag is just as useless as normality or regularity. – user53153 Mar 5 '13 at 16:00
Yes! I mentioned that to M Sina in a comment to one of the edits, but apparently that comment was unnoticed. Completeness is overly broad, similarly I think that diagonalization is bad. – Asaf Karagila Mar 5 '13 at 17:39
@Asaf: can you post a separate request for diagonalization? Exposing my ignorance here, besides the Cantor variety and the one in linear algebra/functional analysis, what other things are called diagonalization? – Willie Wong Mar 6 '13 at 9:48
@Willie: Cantor's method extends pretty much everywhere in logic and set theory. Godel's incompleteness proof is essentially by diagonalization, for example. – Asaf Karagila Mar 6 '13 at 9:51
@Asaf: Would it be acceptable to have two tags instead: (matrix-diagonalization) and (cantor-diagonalization)? – Willie Wong Mar 6 '13 at 9:54
@Willie: I don't see why the set theoretical counterpart needs a tag to begin with; but I also don't see why the linear algebra one needs a tag either. – Asaf Karagila Mar 6 '13 at 9:55
@Asaf: just fishing for ideas. – Willie Wong Mar 6 '13 at 9:57
I am not a lake. Or a river. :-) – Asaf Karagila Mar 6 '13 at 9:58
Fine. I posted that as another answer. – Asaf Karagila Mar 7 '13 at 18:16

By the tag wiki, it looks like and are being used the same way. Should the former be deprecated in favor of the other?

Also, there has been previous discussion on this topic, but it seems that no conclusion was reached.

Should the question be brought up again on meta.math?

EDIT (M.S.): As you have probably noticed, is empty now (already for some time).

EDIT (J.M.): That damn tag has kept popping up the last few days... I've been able to remove it, but it seems I'm the only guy who gives a rat's ass about these things...


Maybe that last bit was somewhat harsh. The thing popping up just had me frustrated. I do remember asking if we can have a blacklist for it, and Willie said that he'd rather hope that people would be smart enough not to use that tag again. Oh well.

(Much later)

I see somebody bothered to write a tag-wiki (again?!) but didn't bother to remove said tag from the questions... maybe I should stop caring; it just raises my blood pressure.

EDIT (M.S.): tag has been blacklisted already some time ago. Most regular users probably know about this, but I guess it is worth adding the information to this post, too.

Ugh. Some of the questions are [abstract-algebra] and some of them are [algebra-precalculus]. That is annoying. – Qiaochu Yuan Jun 26 '11 at 4:15
@Qiaochu: I think a small minority (10% or so) are [algebra-precalculus]. I can go through and help with manually retagging, if you think it's a good idea. – Michael Chen Jun 26 '11 at 4:19
10% from ~600 is still 60 questions. This would cause a tsunami of old questions to wash over the front page if done at once. If you do retag the rogue questions, please limit the amount of retagged questions to 10 or so every day (and please do that in some interval as well to allow new questions rise again). – Asaf Karagila Jun 26 '11 at 6:35
@Asaf: Will do – I will go oldest to newest, 2-3 questions every 4-6 hours. – Michael Chen Jun 26 '11 at 23:49
I'll try to continue in retagging algebra questions. Hopefully doing it twice a week, each time approximately 10 questions, will not cause too much trouble. I know this might be annoying, particularly to the people browsing abstract-algebra and algebra-precalculus tags, but it is probably the only way to do this. (Originally I started at the rate 10-15 questions a day, which was probably too much.) – Martin Sleziak Nov 10 '11 at 16:28
@Martin: thanks for doing this. That sounds very reasonable. – Willie Wong Nov 11 '11 at 11:27
@J.M. I often see that and edit as well, I don't think you're the only one who cares. I was just preoccupied with other things on the site lately... – Asaf Karagila Jul 15 '12 at 11:31
@Asaf, no worries. I see you have your hands full on somebody. ;) – J. M. Jul 15 '12 at 11:33
@J.M. It seems that this time a few questions with the tag were left on purpose - so that the tag-wiki with the warning will not be lost. See here. I'm sorry about your blood pressure. – Martin Sleziak Sep 2 '12 at 7:59

Something that has been bugging me for a while:

There is a tag, while the correct form would be . Given that there are currently only 16 questions in this tag, it won't be too hard to correct this.


Update: has been merged into .

It should probably be root-systems, in plural. You have 6 upvotes and 0 downvotes; I say go for it. – Rahul Sep 15 '13 at 11:51

I find lacking in utility. It seems that every post which has this tag is either closed or could easily be retagged. I would be happy to suggest alternative tags for posts tagged as .

EDIT by Srivatsan (Nov 29): Bumping up the post. I propose that we start removing the tag from posts.

A large portion of those questions need to be retagged manually. A first step maybe to retag the ones that have only numbers and nothing else as the tag. – Willie Wong Aug 18 '11 at 11:37
@Willie Is there a way to find all such questions, btw? – Grigory M Aug 18 '11 at 12:47
@Grigory: not that I know of besides going through the entire list. But for (number), there is only 1 (I just checked now, makes my earlier comment a bit silly). – Willie Wong Aug 18 '11 at 12:55
@Willie I see. (No idea what tags this one should have, but IMO it's offtopic -- voted to close.) – Grigory M Aug 18 '11 at 12:57
number tag is out of the system. – Martin Sleziak Jun 22 '12 at 17:17
BTW the number tag has been blacklisted. – Martin Sleziak Jun 6 at 14:20

In my opinion and recently created tag should be synonyms.

(If the intended use of is different, it should be clarified in tag-wiki, which is currently empty. Based on two questions which currently have this tag, I think the usage is the same as , therefore I made the above proposal. If you think that these two tags should have different purpose, please, explain it in the comments and consider editing tag-wiki.)

I support that, and have suggested a synonym. – Asaf Karagila Jan 4 '12 at 17:41

I think the current tag is not as good as or even better .

Perhaps change them all to (recursion)? – Asaf Karagila Apr 24 '11 at 21:25
The official name I learned from books is recurrence relation, not recursion. – Tim Apr 24 '11 at 21:26
@Tim: The tags, if I recall correctly also dip into recursion theory at times. – Asaf Karagila Apr 24 '11 at 21:42
How are recurrence relation and recursion theory related, and how do they differ? – Tim Apr 24 '11 at 21:50
@Asaf @Tim: since this comment thread is getting off topic, I'm removing the posts to leave the discussion on topic. Cheers! – Willie Wong Apr 26 '11 at 17:32
This is annoying. Some of the questions tagged [recursive] are about recursive functions but some are about recurrence relations. I think this one may have to be done manually. – Qiaochu Yuan Apr 29 '11 at 6:57
If they are about computable function they should be retagged as "computability". I will leave a separate comment about the "recursion theory" tag that should also be merged to "computability". – Carl Mummert May 1 '11 at 22:56
@Tim: they are completely unrelated. I think this tag should be deleted, and its tagged questions retagged. But I don't know whether that can be done without bumping all the questions. – Carl Mummert May 1 '11 at 23:15

I think the posts tagged as can probably be retagged also, and this tag should be deleted.

real-number-computation is empty now. Thanks to Eugene for helping with emptying this tag. – Martin Sleziak Jun 23 '12 at 11:44

Do we need ? Its contents seem... random and unrelated.

Assume by contradiction that we do, since it exists the contradiction hypothesis holds and therefore it is a contradiction!

I propose eradicating this tag completely.


Both and are used for the same topic, the later has now a nice tag-wiki (thanks to Alexander Gruber). I think they should be synonyms.

EDIT: They are synonyms now. (Thanks to Willie Wong.)

It seems that this proposal has received some support. Unfortunately, I do not have enough reputation in either of the two tags to be able to suggest a synonym. (You need at least 5 upvotes.) – Martin Sleziak Mar 18 '13 at 6:30
I've merged the two tags and made them synonyms. – Willie Wong Mar 18 '13 at 9:20
@WillieWong Thanks for doing that. Should this post be deleted, so that the thread is not too long? (At least for <10k users.) – Martin Sleziak Mar 20 '13 at 18:17
Sure! Off and on I've been cleaning up this thread by deleting completed requests. I've not had the opportunity recently to go through them and edit all the changes into the ChangeLog answer, however, and I apologize for my lack of time. – Willie Wong Mar 21 '13 at 7:46

Please merge (66q) into (2q), so as to match the established tag pluralisation convention.

The tag wiki and excerpt from are better, though, so maybe they need to be carried over somehow.

Update: This merge has been processed. Thanks Arthur Fischer!

I was coming to post this request. Perhaps the right way to do it is to merge the new into the old, and then rename the old one. – Asaf Karagila Oct 30 '13 at 5:29
So this seems unproblematic and uncontroversial. I'll go ahead an transfer paradox's tag-wiki and excerpt to paradoxes, and then merge/synonymise.... [3 mins later: done] – arjafi Nov 1 '13 at 18:03

The two tags, (eigenvalues) and (eigenvectors) have now both been marked as synonyms to . I have to remove the word "and" from Douglas Stones's suggestion because of the 25 character length limit on tag names.

I don't see the need for having both and as separate tags.

Potential names for the merged tag: (eigensystems), (eigenanalysis), (eigendecomposition). If there are better terms for this, please propose them in the comments.

Here is some relevant empirical data from the Google Ngram Viewer.

I like Douglas S. Stones's suggestion (eigenvalues-and-eigenvectors), which neatly mirrors the existing tag .

May I then propose the more general eigensystems if these two are merged? – J. M. Sep 20 '11 at 7:14
@J.M.: Eigensystem, eigenanalysis, eigendecomposition... Is there a standard established term for this? – Rahul Sep 20 '11 at 7:27
@J.M., Rahul: We can go informal with [eigen-stuff] :-) – Asaf Karagila Sep 20 '11 at 7:37
"Eigendecomposition" is sorta kinda long, so I'd go with "eigensystem" myself. But I'm down with an explanation of why other terms would be better... – J. M. Sep 20 '11 at 7:45
@J.M.: I added some empirical data up there. But looking at it I still can't form a clear opinion on which is best. – Rahul Sep 20 '11 at 8:11
I personally like (eigen-decomposition) better as the primary tag. I can of course Syn. eigensystem, eigenvalues, eigenvectors all to the primary tag, whichever it is that we choose in the end. – Willie Wong Sep 20 '11 at 14:21
Perhaps [eigenvalues-and-eigenvectors]? I think [Eigen-decomposition] would not immediately suggest eigenvalues and eigenvectors to e.g. students encountering eigenvalues and eigenvectors for the first time. – Douglas S. Stones Sep 15 '13 at 11:22

I'm not too keen about the tag; something like might be more suitable, unless one has a better name for the tag we can assign to calendrical questions.

I am somewhat tempted to just delete the tag altogether. A lot of the birthday questions are just probability/combinatorics. Much of classical mathematics (esp. those developed with relation to astronomy) are actually closely tied to the study of calendar systems, but of the questions currently with the birthday tag, I don't think any falls in that category. – Willie Wong Apr 16 '11 at 18:25
@Willie: I won't mind a deletion; I threw this out because I'm not comfy with it, but have no solutions (to propose) for it. – J. M. Apr 16 '11 at 18:27
I've removed the birthday tags from most of the questions, and added a 'calendar-computations' tag for the few that is appropriate (if the question's answer uses the Doomsday algorithm in some way, for example.) – Willie Wong Apr 16 '11 at 18:35
@Willie: Sounds good to me. :) – J. M. Apr 16 '11 at 18:39

I find the tag unneeded, with only 11 questions tagged under it, some of these questions belong to (however tagged under ) and others fit well under currently available tags.

I see no actual use of the tag for real questions that are not fitting well and properly under other tags of the currently tagged questions.

It should be deleted after verification that all questions fit under other tags currently present, personally I think it is fine (except for one question tagged only under which I am uncertain how to classify).

I think most natural-number questions would fit well in elementary-number-theory. – Henning Makholm Nov 23 '11 at 15:24

The tag was recently created. We used to have an tag, but we decided that it was sufficiently covered by , and so was merged into several months back. In keeping with this decision, I think should also be merged with .

I just looked at the questions tagged with (expected-value). It appears to me that a couple of them perhaps should be tagged (probability-theory) instead of (probability). What do you think? – Willie Wong Sep 19 '11 at 18:18
@Willie: Good point. Of the 5 that are currently tagged expected-value, I think the two that are also tagged (probability-theory) should still be tagged (probability-theory) and not also tagged (probability). The other three should be tagged (probability). – Mike Spivey Sep 19 '11 at 19:45
@Willie: I removed the "expected-value" tag from the two that should be tagged "probability-theory." It should be fine now to merge "expected-value" with "probability." – Mike Spivey Sep 21 '11 at 22:58
Okay, I've made the merge. – Willie Wong Sep 22 '11 at 1:02

I am very much unfamiliar with the topics, however do we really need both and ?

As we agreed that is better, I wonder... what is the difference between that and ? I'm certain that some difference exists to justify the two tags to be separated. Is it possible for someone to write it into the Tag Wikis (esp. into the excerpts) to help [me] distinguish between the two?

Edit II:
The tag came back. I tried synonymizing it with , alas I could not since there is only one question in the tag with one vote and no answers. So in fact, no one can suggest a synonym!

Both should become (low-dimensional-topology), maybe? – Grigory M Aug 18 '11 at 10:21
@Grigory: I like that idea. – Willie Wong Aug 18 '11 at 11:36
(Re: edit) Huh? Most questions in manifolds about manifolds of arbitrary dimension and have nothing to do with low-dimensional topology. (In any case, adding tag wikis would be nice, of course.) – Grigory M Aug 18 '11 at 12:09
@Grigory: I figured as much, I don't really know the difference. Since the original tags were 3/4-manifolds, I would expect this all to have something to do with manifolds... – Asaf Karagila Aug 18 '11 at 12:12
@Grigory: one might think about merging (manifold) into (differential-geometry) (I don't really see the difference). There is some cleaning up required before doing so, though. – t.b. Aug 18 '11 at 12:14
@Theo: Are you that one? :-) – Asaf Karagila Aug 18 '11 at 12:16
@Asaf: well manifolds can have any dimension you like :) low-dimensional topology is specifically knot theory, 3-manifold and 4-manifold topology. E.g. Thurston, Freedman, Donaldson, Witten to name a few of the most famous guys (you know Perelman, I guess). – t.b. Aug 18 '11 at 12:17
@Asaf: I didn't quite get your joke. No I was just tagging a few obvious candidates (and one false positive) with the new (low-dimensional-topology) tag. Before I go ahead I'd like to see others' opinion. – t.b. Aug 18 '11 at 12:19
@Grigory: that's what I meant with cleaning up. – t.b. Aug 18 '11 at 12:20
No, (manifolds) should not be merged into (differential-geometry): manifolds are not required to have a smooth structure. Low dimensional topology has a set of tools separate from higher and lower dimensional topology. In one and two dimensions, one can always equip manifolds with a smooth structure, and those smooth structure always give rise to Riemannian/conformal structures, so topology is completely determined by geometry. In higher dimensions the topology is too malleable that a lot of weird stuff can happen. 3 and 4 dimensions is "just right". – Willie Wong Aug 18 '11 at 12:27
@Willie: can we move this discussion here? – t.b. Aug 18 '11 at 12:32
For example, you can think about the equivalent of the Poincare conjecture in all dimensions. Dimension 1 is trivial. Dimension 2 is contained in Riemann mapping theorem. Dimension 5 and higher can be dealt with using h-cobordism. Dimension 4 was solved separately by Freedman, and dimension 3 Perelman's proof uses so much geometry that it leaves some topologists unsatisfied. – Willie Wong Aug 18 '11 at 12:34

Shouldn't and be synonyms?

Updated: As Willie Wong suggests, the more general tag "convexity" would probably be even better.

Updated, again: On further reflection, I think is the better general term. We already have 9 other tags called "[something]-analysis", and so would be more consistent with our already-existing tags than would.

I wonder if a more general name like "convexity" would be a better umbrella term. What do people think? – Willie Wong Oct 3 '11 at 12:37
I'm down with convexity, unless you guys have better suggestions... – J. M. Oct 3 '11 at 12:42
@Willie: Since nobody else has weighed in on this, why don't you go ahead and make either "convex-analysis" or "convexity" the general term, depending on whether you are convinced by my last update to my answer. :) – Mike Spivey Oct 5 '11 at 3:31
Done. Now if Mike or @J.M. will propose a Tag-wiki for convex-analysis, we'd be all set. (I opted for convex-analysis after realising that we still have a very useful third tag (convex-optimization) which I don't think should be merged with these two.) – Willie Wong Oct 5 '11 at 13:52
@Willie: Thanks. I'll propose a tag-wiki for convex-analysis. – Mike Spivey Oct 5 '11 at 16:21

is quite the mess; some of it is for inverting matrices and some of it is for inverting functions. I'm not really pushing for a deletion, but is there a neat way to resolve this?

Added [by Srivatsan]: I propose to delete the tag.

This tag is currently used in a variety of different senses: inverse of a ring/group element, matrix inverse, function inverse, inverse Laplace transform, inverse cdf, etc. However, it seems that all 30 questions under the tag are safely covered by the other tags.

Just classify that as inversion within rings or something that generalizes both instances and more! :-) – Asaf Karagila Aug 8 '11 at 8:12
I don't see the problem: deep below the surface they are all the same thing. I am however in favour of a tag wiki that briefly mentions inversion as an abstract concept and asks the user to specify the regime where the idea is used in the question. – Willie Wong Aug 18 '11 at 11:40

This is a good initiative. Please have a look at my old question and make decisions for the tags mentioned therein.

I can create the synonyms, but I'm not sure I can change the master tags if they're not already created without bumping a question. I'll think about it. – Qiaochu Yuan Dec 22 '10 at 4:50
@Qiaochu: at least in SE 1.0, you can rename a tag with a completely new name, but it's pretty counterintuitive: "If the Remove Tag does not exist, the Master Tag will be renamed to the Remove Tag." See also… – Anton Geraschenko Dec 22 '10 at 19:08

There is a tag. I feel it can be merged with the tag . Can a moderator implement this?

I can't really claim appropriate expertise here, but on a quick skim, at least a few of the questions tagged [counting] do not seem like combinatorics questions (though certainly the majority do seem like combinatorics questions). – Isaac Mar 6 '11 at 6:12
This question has been discussed before (although I can't remember where now). There actually is a formal proposal on the tag synonyms page ( to make "counting" a synonym for "combinatorics". Users with 2500+ rep can vote this up or down. – Mike Spivey Mar 7 '11 at 17:11
@Mike You probably meant this discussion: On the (combinatorics) and (counting) tags.. – Martin Sleziak Jul 17 '12 at 7:28

Can anybody give a good reason why the and tags are separate? I would say retain one or the other, but certainly not both.

As an additional note: I think [numerical-linear-algebra] is too specific a tag; better that the questions have both the [linear-algebra] and [numerical-(whatever)] tags. – J. M. Apr 7 '11 at 9:02
M. I don't think there is a way we can replace one tag with two. So some one will have to go through the numerical linear algebra tag and re-tag every one of them manually. – Willie Wong Apr 7 '11 at 9:32
I've made numerical-methods and numerical-analysis synonyms. – Willie Wong Apr 7 '11 at 9:34
Thank you very much, @Willie. – J. M. Apr 7 '11 at 9:36

Are we ready to follow up the suggestions in the following answer?

The tags [recursive] and [recurrence-relation]

Didn't someone already do this manually? – Qiaochu Yuan Jun 9 '11 at 9:11
No, please look at Carl's answer. There are some small modifications to be done which can only be done by a moderator. – Yuval Filmus Jun 9 '11 at 13:24
Okay, I think that's it. – Qiaochu Yuan Jun 9 '11 at 15:54
Thanks for bringing this up, Yuval. Are all of Carl Mummert's suggestions now implemented? – Mike Spivey Jun 9 '11 at 19:23
The first and third are. The second and fourth are "prescriptive community norms", so it is up to us to implement them. – Yuval Filmus Jun 11 '11 at 22:17

Do we really need , , and as three separate tags?

What is the probability for a question to have any of them? :-) – Asaf Karagila Jul 13 '11 at 16:47
I suppose we should retain (probability-distributions) and subsume/synonymize the other two... – J. M. Jul 23 '11 at 19:00
@J.M.: I agree. – Mike Spivey Sep 3 '11 at 20:36

We all appreciate the importance of but how needed is this tag?

Almost 70 questions are using this tag at the moment, so it will take some work to remove it. (If that will be the outcome of voting on your answer.) – Martin Sleziak Aug 26 '12 at 3:26

Not the answer you're looking for? Browse other questions tagged .