# Help cleanup tags!

This is meant to agglomerate tags that need (occasional or regular) cleanup. That is tags that mean multiple unrelated things and need to be separated into more specific tags. Please follow the examples below and discuss specific needs in comments or separate questions, as necessary.

Conversely, some subjects are scattered over several tags and there it might make sense to merge some tags and to create synonyms. Proposals for such can also be added as answers.

As of August 8, 2017, the length limit for tags went from 25 characters to 35 characters. So now is a great time to allow inconveniently compressed tag names to stretch out a bit...

PS: If you want to cleanup these tags, please keep your rate down to a few posts per day so that your edits don't clutter the main page. Also note that merges can be done by moderators in one go without bumping questions. Thus, it is usually better not to carry out non-minimal merges manually (where non-minimally could mean more than three to five).

• Can you simply delete all tags that have < x followers, where x is a positive integer the moderators set? – Bill Johnson Sep 24 '13 at 1:08
• @Bill: That would delete a lot of seldom used tags, which is not the intent here. – François G. Dorais Sep 24 '13 at 1:10
• Maybe not, François, but it would help to delete these tags. – Bill Johnson Sep 24 '13 at 1:48
• @BillJohnson, another objection is simply that many people don't use the 'favorite' and 'ignored' system, but tags are still useful to them. I don't think there's any guarantee that every "interesting-to-someone" tag is actually a 'favorite' of anyone. – Scott Morrison Sep 24 '13 at 1:59
• I completely agree with @BillJohnson that there are too many tags and I think we should try to get rid of quite a number of them. One could discuss what is the best way to go about this, but that there are too many tags for me is a given. (And I write this as someone who actually read the pages over pages of tags, more than once.) – user9072 Sep 24 '13 at 12:44
• By the way, is there a particular reason why MO uses its own classification of subjects in mathematics rather than a tag system along the lines of the MSC (ams.org/mathscinet/msc/msc2010.html)? – Stefan Kohl Sep 24 '13 at 13:28
• @StefanKohl MO uses the (simpler) arxiv classification. – François G. Dorais Sep 24 '13 at 13:41
• Only a small part of the tags are actually arxiv tags. -- The arxiv classification doesn't go very much into detail, which is -- besides the easiness of creating new tags -- probably the reason for the many additional tags, including tags with unclear meaning and outright 'clutter tags' (though some of the latter have been removed in the course of the thread meta.mathoverflow.net/questions/642/…). – Stefan Kohl Sep 24 '13 at 15:32
• @StefanKohl: Yes, feel free to ask for the deletion of some clutter tags. (It's best to ask a question on meta since a some users like to assist in cleanup efforts.) – François G. Dorais Sep 24 '13 at 15:42
• @FrançoisG.Dorais: I think the main point are not single inappropriate tags. Contrary to the top-level arxiv categories, the MSC is already fully-thought reasonably complete standard classification, and I think adopting it for MO would probably remove the need to think about adding or removing tags, about which tags are appropriate and which are not and about which tag means what. Or do you see a reason for MO's partial reinvention of the wheel here? – Stefan Kohl Sep 24 '13 at 15:53
• @StefanKohl: Users are able to create their own tags. The system was seeded with arxiv tags to get things going but there was no long-term plan to keep them. The main problem with MSC is that it's too large. – François G. Dorais Sep 24 '13 at 16:00
• @FrançoisG.Dorais: Sure, there are 4 or 5 times as many 5-digit MSC numbers than tags in MO -- but contrary to MO tags, the MSC is an hierarchical scheme. Thus if e.g. using two of the three levels is sufficient for MO, one could well restrict to that. – Stefan Kohl Sep 24 '13 at 16:14
• @StefanKohl, one problem with MSC numbers is that they are unintuitive numbers and so except for the ones I use frequently, I would not recognize most of them. – Benjamin Steinberg Sep 24 '13 at 17:12
• @StefanKohl, the OP would still need to look up the code before posting. – Benjamin Steinberg Sep 24 '13 at 20:49
• @BenjaminSteinberg: actually, they wouldn’t need to! The auto-complete system here is clever enough that if a tag is called e.g. “54-XX-general-topology”, it will be suggested when you start typing “topology”. Honestly, that would give a better lookup interface for the MSC than the current official ones… – Peter LeFanu Lumsdaine Oct 8 '15 at 14:53

The tags and are (unsurpsingly) used for both the 'order' and the 'geometric' meaning.

(I am not sure what to do here; perhaps it deserves a full question, but I thought I'd post here first to get some initial reaction.)

• There was an old discussion on tea about this. – François G. Dorais Jan 15 '14 at 15:27
• Thanks for pointing this out, I should have known/checked. Yet, while in some sense there were even two: in the very old tea.mathoverflow.net/discussion/679/lattices Ryan Budney suggested upon Mariano mentioning the problem, to have lattice-poset and lattice-subgroup In tea.mathoverflow.net/discussion/1375/… the issue is somewhat different as I think in that request the order meaning was ignored and the issue was distinguishing between really geometric objects and more algebraic things (vaguely), and there is euclidean-lattice for the former. – user9072 Jan 15 '14 at 16:38
• Oh I forgot to finish my idea... While the subject came up there was not much discussion and/or they were somewhat inconclusive (regaridng the matter I have in mind) except for Ryan's (IMO, good) idea that never got implemented though. – user9072 Jan 15 '14 at 17:58
• For this, we should fix the terminology everywhere in mathematics, not only on the MathOverflow website. Also, let's fix "field" too while we're there. – Zsbán Ambrus Apr 9 '14 at 9:46
• @ZsbánAmbrus what do you want to express precisely? – user9072 Apr 9 '14 at 14:38

There is a built-in system to automatically create tag synonyms by the nomination and voting of high-reputation users. Unfortunately, it appears that hardly anyone ever looks at this page (and the qualifications for voting are fairly demanding), so I'm posting it here to try to get it more attention. In particular, all of the synonyms marked as "pending" are languishing in neglect until they get four people (or a moderator?) to vote for them, though I think some of them are going the wrong direction.

• It might be worth adding that to vote one needs to (at least I think so) click on the left tag of the two to get to its page where the voting possibility is. – user9072 Dec 9 '14 at 19:10
• There is no way to discuss the synonyms suggested through this system, or is there? – Emil Jeřábek supports Monica Dec 9 '14 at 22:28
• @EmilJeřábek for all I know, no. If you do not approve of one, you can downvote it, and if it reaches score -2 (or something like this) it is deleted. – user9072 Dec 11 '14 at 17:40

The tag is mainly used for questions in a probability context but there are some other "Gaussian" things in there too, e.g., Gaussian binomial coefficients, Gaussian integers.

Perhaps, the current tag should be renamed to something more specific, like gaussian-distributions or gaussian-variables or something along these lines (not sure, suggestions welcome). And the (few) existing ones where it then does not fit could be retagged.

Note there is also a tag .

• Is the dv against the renaming or against the tag being reserved for the prob context. Or against still something else. In any case it would somehow help the discussion if such things where communicated else it is anybodies guess what is the intent. – user9072 Sep 27 '13 at 16:46

As of August 8, 2017, the length limit for tags went from 25 characters to 35 characters. So now is a great time to allow inconveniently compressed tag names to stretch out a bit...

Perhaps we could collect here list of tags which now, after the character limit for length of tag name has been extended, could be spelled in full instead of a shortening. (This answer is CW - feel free to edit in here various tags that are currently shortened.)

Among possible suspects are the tags with name of length 25 - they can be found by this SEDE query: Tags with given length of name. (However, not all shortened tags use exactly 25 characters. Two examples are or .)

Shortenings to be expanded

• vs. (Both names should be kept here with a synonym in one or the other direction. After all, people around here know what GCH is, so it probably can remain the master tag. But adding a synonym might be useful addition, since people looking for the tag corresponding to their might start to write something liked "continuum hypothesis" in the tag field.)
• $$\to$$ (Maybe the shortened name could be kept as synonyms - since MO users are probably used to it by now?)

Synonyms with names longer than 25 characters

1There is a separate discussion whether there could be a better name for this tag: The tags (transcendence) and (transcendental-number-theory).

• As I was not sure how to "expand" (combinatorial-hopf-algebr), (differential-graded-lie-a) and (infinite-time-computabili), I'm leaving suggestions for this tag to users who are more familiar with these areas. – Martin Sleziak Aug 9 '17 at 18:07
• In case it is useful for somebody, here is query for tags with length at least 20. (Of course, you can easily change 20 and 25 to other numbers.) – Martin Sleziak Aug 10 '17 at 3:49
• We have a tag (cartesian-closed). With a longer character limit, we could have (cartesian-closed-categories). Was this the intended meaning of this tag? Or is cartesian closed commonly used also in some other meanings? – Martin Sleziak Aug 12 '17 at 4:57
• BTW (topological-quantum-field-theory) fits the new 35 characters limit. Would maybe a synonym (topological-quantum-field-theory) $\to$ (tqft) make sense. (It might help people to find the tag, if they start typing "topological quantum field theory" in the tags field when asking a question.) – Martin Sleziak Sep 8 '17 at 3:34
• Actually I think that gch should be made a synonym to continuum-hypothesis, and the usage guidance the latter can obviously encompass the generalized one. And "people around here know what GCH is": no, I know quite many people in pure math who would not identify "GCH" without further context. – YCor Mar 4 at 21:52

The tags matrix-analysis (32 questions tagged) and matrix-theory (18 questions) should probably be merged, unless there is a strong difference between them that I am not aware of (incidentally, there is also matrices, 150 questions tagged).

The tag matrix-inverse (6 questions) seems overly specific and in my opinion it should be removed outright.

• There is also matrix-equations but there is no matrix-algebra. I don't know what the differences could be; I hope somebody will explain. Are these tags used in significantly different ways? – François G. Dorais Jan 16 '14 at 4:32
• The ones I have heard in real life are: "matrix analysis" for the study of matrix inequalities and advanced linear algebra (e.g. [[1]](amazon.com/Matrix-Analysis-Graduate-Texts-Mathematics/dp/…)); matrix functions and matrix equations (mostly numerical/applied; e.g. [[2]](mims.manchester.ac.uk/events/workshops/FUN13)). "matrix algebra" is not that common and typically used by non-mathematicians. "matrix theory" sounds strange to my ear. – Federico Poloni Jan 16 '14 at 5:29
• My suggestion is as follows: make matrix-theory a synonym of matrix-analysis; I could consider merging them both into matrices, although that's a bit generic; Stet matrix-equations, remove matrix-inverse – Federico Poloni Jan 16 '14 at 5:32
• re matrix-theory: I think this is an instance of a sort of general MO phenomenon, users add 'theory' to distinguish it from just the 'thing' that is perhaps too generic as a tag; we had some discussion on order-theory. For some q tagged matrix-theory it seems matrix-analysis would not fit. One could go over the list though and extract these things relatively quickly. For matrix-inverse, I am in favor of getting rid of it yet via a synonym, else people will recreate it, or even worse use just inverse which should also be listed here in fact. – user9072 Jan 16 '14 at 13:14
• There are also various other tags containing matrix and matrices some very little used. Would you have an opinion on some more of them? – user9072 Jan 16 '14 at 13:16
• Personally I'd keep matrices, random-matrices, matrix-analysis, nonnegative-matrices, matrix-equations and maybe sparse-matrices. I don't know what r-matrix refers to; if it's short for "random matrix" then merge. m-matrix and copositive-matrix can be merged into nonnegative-matrices. adjacency-matrices and matrix-tree into some variant of graph-theory I guess (not an expert). nilpotent-matrices, circulant-matrices, orthogonal-matrices seem too specific. – Federico Poloni Jan 17 '14 at 2:56
• We should look for more opinions though, there are surely lots of other people with different viewpoints than mine on "matrix stuff". – Federico Poloni Jan 17 '14 at 2:58
• Thanks. This looks good to me. The tag r-matrix was created for something called "R-matrix" in quantum algebra/groups (I don't know what it is though). It was misused a bit though. I think/hope I 'cleaned' it just now, and it is just this qa thing now, which one might keep (but I cannot tell); preferably with a tag-wiki so it does not get used again for dealing with matrices in the software R... For matrix-tree this is uniquely used and not even very relevant where it is used, I would simply remove it; for adjacency-matrix one could set up a synonym into algebraic-graph-theory – user9072 Jan 17 '14 at 10:53
• Also talking about matrices, @FrançoisG.Dorais now that we have sysnonyms could you please set up the synonym matrices <--- matrix I think there is some risk of people not finding the tag due to the (unusual) plural. – user9072 Jan 17 '14 at 10:56
• thanks for the retagging effort @quid. – Federico Poloni Jan 17 '14 at 11:10
• @quid: When a tag doesn't exist, I don't think I have a quick way to create a synonym so it's just as easy for you to suggest it as it is for me. – François G. Dorais Jan 17 '14 at 17:01
• @FrançoisG.Dorais oh, I was not aware of this, and I have to confess the fact that I can suggest syns did not really sink in either. I will try it some time soon and in the meantime voted on the syn. But also, while in this case it is true I could have suggested it, this is not always the case as a user (besides globally enough points) needs some score (namely 5) in the tag. – user9072 Jan 18 '14 at 1:15

I suggest deleting the tag .

I would guess that the tag was intended to be about the decomposition theorem of Beilinson-Bernstein-Deligne-Gabber. It seems unnecessary to have a whole tag just dedicated to this theorem ( should suffice). What's worse, most posts with this tag are just about various "decompositions" in any area of mathematics.

• Do you think that (perverse-sheaves) tag should be added to some of the posts which are tagged decomposition-theorem but not preverse-sheaves? I have asked a moderator (Todd Trimble) about this tag not too long ago. Since he suggested simply removing (decomposition-theorem), after the removal some of those questions might be missing the relevant tag. – Martin Sleziak Jun 10 '18 at 5:58
• Hi Martin. I took a look and there are two questions on that list related to the BBD decomposition theorem and perverse sheaves: mathoverflow.net/questions/128822 and mathoverflow.net/questions/1039 . I guess those two could be retagged but I wouldn't consider it urgent (they have other accurate tags). – Dan Petersen Jun 10 '18 at 6:32

The tags and should be merged; the first being more used, and also in analogy with the tag , I'd suggest to embed into .

Making a synonym $\to$ would also have the advantage that the latter tag is suggested when people type "ring". (Note: has already been embedded in .)

• Re: does not include the word "ring" in its wiki, and hence is not suggested when people type "ring". In fact, the tag-wiki does not influence whether the tag is shown when you type something in the tag field. This is influenced only by tag names (including tag synonyms). – Martin Sleziak Feb 18 '18 at 15:59
• @MartinSleziak right, thanks. Btw the edited tag-wiki for noncommutative-algebra now mention rings, but this means that it will be suggested from typing rings only when they'll be made synonyms. – YCor Feb 18 '18 at 16:10
• I have edited your post to correct the information saying when the tag is suggested. (And to some extent also to make your post shown if somebody views the last activity in the question.) When you have time, please do edit the post further to get it to the form you are satisfied with. – Martin Sleziak Feb 19 '18 at 7:22
• I've never been convinced about this one and it's been nearly a year. It's still not clear what to do here. – François G. Dorais Jan 19 at 23:34
• @FrançoisG.Dorais it's also unlikely that anybody might suggest anything more convincing to you if you don't say why you're not convinced. – YCor Jan 19 at 23:41
• They both have tag descriptions and they don't match: one explicitly includes non-associative algebras and the other explicitly includes commutative rings. It seems somebody thinks the two are slightly different. – François G. Dorais Jan 19 at 23:49
• @FrançoisG.Dorais it guess just means that these tags were written by two different persons without comparing to the other one – YCor Jan 20 at 0:22
• Just for the convenience of the people who stumble upon this post, I will mention that there is now a separate question about these two tags: Noncommutative rings/algebra tags. – Martin Sleziak Jan 20 at 17:15
• @MartinSleziak yes of course you're right, thanks! – YCor Jan 20 at 18:07

Done

I propose to deprecate . It seems redundant with other tags, very broad, and the usage seems inconsistent.

I feel it is comparable to the meanwhile removed and the deprecated .

(Explication on terminology: To deprecate a tag is not a technical measure. What it means is that the tag-description is changed to say this tag should no longer be used. Over time it could then be slowly phased out via retagging.)

Done

I propose to deprecate . It seems redundant with other tags, very broad, and the usage seems inconsistent.

I feel it is comparable to the meanwhile removed and the deprecated .

(Explication on terminology: To deprecate a tag is not a technical measure. What it means is that the tag-description is changed to say this tag should no longer be used. Over time it could then be slowly phased out via retagging.)

About tag (13 questions at this date).

a) tautological part: should be changed to , in coherence with the use of tags related to Kähler: , ...

b) a bit less important: I think it should even be changed, in coherence with the use of , to . At least, I've checked all 13 questions and all are compatible with using .

• Actually kahler-geometry and hyperkahler-geometry would be even better, since it's more suitable for both considering (hyper)Kähler manifolds, or (hyper)Kähler metrics on a given manifold... – YCor Mar 16 at 23:02

I propose to systematically rename each tag reduced to the name of a software, adding "-software" to make the tag (thus ) more understandable, and, furthermore, to allow to gather such tags when typing "software".

This applies to , , , , etc (this list is not comprehensive; this post is community-wiki hence feel free to complete it).

If for some reason "software" could be replaced by a better word, please propose. Might be or too, I don't know.

• Makes sense but, to play devil's advocate, is there any general confusion going on? Yes, magma is also a math term but this is only one. – François G. Dorais Mar 7 at 0:50
• @FrançoisG.Dorais "gap" is a math term ("spectral gap", "gap between primes"). But I didn't talk of confusion. It would be an improvement because "coq-software" would make the meaning of the tag transparent also to people who never heard of coq, and because of another reason I already wrote. – YCor Mar 7 at 0:54
• I hear that and it makes sense to me. I'm inclined to go ahead but I'll let is sit for a few days in case a counterargument comes up. – François G. Dorais Mar 7 at 0:56

I propose to make (10 questions) a synonym of (34 questions).

has no usage guidance.

has: A quadratically constrained quadratic program (QCQP) is an optimization problem in which both the objective function and the constraints are quadratic functions.

The latter could be embedded, possibly improved, as usage guidance to the former.

A tag with initials is, I think, not suitable and should systematically be proscribed. (Typing quadratic as a tag does not suggest qcqp, which is a problem... and a tag is supposed to convey information to other people than its bare users.)

Hence, if there are serious reasons not to make synonyms, should be renamed; would be a compromise. Of course I prefer the previous option (make a synonym).

More generally, I'd propose to systematically rename each tag reduced to initials (please add examples if you can think of), or to the name of a software (I'll ask a separate question for the latter).

Edit: given Rodrigo de Azevedo's feedback, I suggest to rename as (the whole exceeds the 35-character limit (43 characters); is exactly 35).

• Re: More generally, I'd propose to systematically rename each tag reduced to initials. Several suggestion on expanding tags to longer names are collected in this answer - moest of those have already been done. – Martin Sleziak Mar 4 at 17:41
• BTW I have pinged the tag creators of those two tags - in case they have something to add to this discussion. – Martin Sleziak Mar 4 at 17:50
• About acronym tags, I always thought that tags stands for "Tags And General Stuff". – Asaf Karagila Mar 5 at 18:14
• I created the QCQP tag. I do not see how it makes any sense to make QCQP and QP synonyms. They are very different. The feasible region of a QP is a convex polytope or an affine space. The feasible region of a QCQP can be a finite set of points. However, I agree that "qcqp" is not easy to find and I would certainly not object to renaming it "qc-quadratic-programming" (if the tag is not too long for MO). – Rodrigo de Azevedo Mar 10 at 11:27
• @RodrigodeAzevedo thanks; I edited accordingly. – YCor Mar 10 at 11:37
• This is a tough one. A priori, I think it's a bad idea to shorten the first word to just "q"; I'd rather have the second, third or later words abbreviated since it's hard to imagine anyone would want to autocomplete "q-" this way. @RodrigodeAzevedo any thoughts? – François G. Dorais Mar 28 at 3:48

Done.

The tags and should surely be synonyms. I would personally prefer that the former (much older, well-established, and less ambiguous, terminology) be the tag and the latter the synonym, but either direction of synonym would be better than having two separate tags.

seems to have no coherent use. It has 3 watchers for 88 questions, which is a very low ratio (compared to tags with a comparable number of questions).

It's mostly to mean some use of continuity, often somewhere fitting with , , and others. This number of questions is ridiculously small compared to the number of questions where the word "continuous" appear ($$\ge 11000$$), or "continuity" ($$\ge 2000$$).

Therefore, I'd suggest to deprecate, and even to burninate.

• Do you have a good deprecation message to suggest? – François G. Dorais Mar 28 at 3:43
• I will just point out that your second paragraphs suggests that the tag would help find posts which are about continuity - as opposed to finding posts where continuity is merely mentioned. (Of course, only if the tag was actually used consistently. I have expanded this a bit here in chat.) This is intended more as a general remark - I do not have strong opinion about this specific tag on MathOverflow in either direction. – Martin Sleziak Mar 28 at 5:21
• @FrançoisG.Dorais By "deprecation message" you mean the tag warning which would be displayed when somebody attempts to use the tag? – Martin Sleziak Mar 28 at 7:59
• @MartinSleziak having a quick look at the 50 first questions tagged continuity, I'd say that at most 5 discuss continuity as a concept. And 5 is an upper bound, there's not a single one for which I'm sure it qualifies (an example which qualifies, but is not tagged continuity: mathoverflow.net/questions/182300/…). – YCor Mar 28 at 8:08
• @FrançoisG.Dorais Deprecated; do NOT use this tag. Instead you could consider real-analysis, gn.general-topology, fa.functional-analysis or related tags. – YCor Mar 28 at 8:10

The tag has a number of completely different questions. There's a definition in probability theory, as an increasing sequence of $\sigma$-fields. There also appears to be some completely different meaning in homological algebra or some other areas (too far from my own for me to understand).

Is this notion worthy of its own tag in any of these cases? (For probability I don't think filtrations need their own tag; I'd just use .) If so, a more specific tag should be made and an appropriate wiki written. If not, then perhaps the tag should just be destroyed.

• The probability theory notion and the algebra notion are actually essentially the same (a nested chain of substructures), though in practice the ideas needed to think about the two are pretty much unrelated. – Eric Wofsey Oct 8 '15 at 21:29

I'm not sure if this is the right place to raise the issue, but I don't really like that has been merged with . In my opinion, this is the same (in a smaller scale) as merging combinatorics into discrete mathematics. There are many problems in discrete-geometry that have nothing to do with combinatorics.

• That merger was done on December 15, 2014. We can't undo the merger but we could remove the tag synonym to allow future uses of combinatorial-geometry. A test for doing this is to propose a tag info blurb which demonstrates how the two tags are different. – François G. Dorais Aug 3 '17 at 22:28
• @Francois So I should propose a tag info for combinatorial-geometry? I would write something short and simple, like Combgeo. is the study of combinatorial problems that involve geometry. Btw, how can the description of discrete-geometry include that "It is closely related to [...] combinatorial geometry" if the latter is a synonym of the former? – domotorp Aug 4 '17 at 8:47
• I'm not sure I can see a problem. For the distinction it's enough to use either the tag "discrete-geometry" or the combination of "discrete-geometry" and "co.combinatorics". – YCor Feb 18 '18 at 19:27
• @YCor Then this should have been done when the merger happened, right? Not to mention that I don't recall seeing anyone ever applying both tags. I also don't think it's good to make people double-tag almost all the time, because a large part (but not all) of discrete geometry is combinatorial geometry. – domotorp Feb 19 '18 at 13:44
• @domotorp co.combinatorics is a top-level tag so basically every question pertaining to combinatorics gets this tags (unless it has comprises too many topics, but this concerns a very small minority). Usually when anybody ask such a question without tagging combinatorics, somebody adds the tag. As discrete-geometry, the topic makes the tag natural, and also it is regularly added. Adding another tag which basically is relevant iff two other wider tags are simultaneously relevant, would in practice just increase entropy. – YCor Feb 19 '18 at 14:26
• @YCor I would challenge the statement that every question pertaining to combinatorics gets the tag. Check graph-theory; the majority of the questions doesn't have co-combinatorics: mathoverflow.net/questions/tagged/graph-theory – domotorp Feb 19 '18 at 21:48
• @domotorp some people say that every question in graph theory should also be tagged combinatorics. In any case, a very large majority of these questions would perfectly fit in co.combinatorics – YCor Feb 19 '18 at 21:55
• @YCor That's my point - people still don't label them co.combinatorics, so you also shouldn't expect people to label the ones that have combinatorial-geometry or discrete-geometry. – domotorp Feb 20 '18 at 7:23
• I know it's hard to rely on a good labeling and acquainted users can help by editing tags. In any case, in such situation the entropy (I mean the mess) is an increasing function of the number of relevant tags. – YCor Feb 20 '18 at 15:45
• @YCor and domotorp: This is (to some extent) related to discussion about (graph-theory) and (co.combinatorics): Which “non-arxiv” tags are de facto top-level tags? Of course, if we strictly follow the guidelines pointed out on MathOverflow Meta every question should have a top-level tag In reality, the top-level tag is missing on roughly 20% of questions. – Martin Sleziak Feb 28 at 5:31

There are tags and . Neither has a wiki or guidelines for usage. The tag seems to be more popular. Should these be merged?

• Are these really the same? – François G. Dorais Jan 19 at 22:57
• Not exactly the same, but quite closely related. I no longer remember if they are used in distinct ways. I think adding tag wikis would be nice, if one chooses to not merge them. – Tommi Jan 20 at 6:58
• Better provide numbers. laplacian: 165 questions. laplace-equation: 16 questions. – YCor Mar 18 at 21:32
• Laplace equation has a precise meaning, namely refers to a classical PDE (laplacian equals zero). I see no particular problem to keep it separate. – YCor Mar 18 at 21:34

I propose to merge and . The latter is used for the same types of questions as the former, and most questions with the latter have little to do with the stable homotopy category per se, as opposed to the model category or ∞-category of spectra.

I think it might make sense to make a synonym for . Although non-convex polytopes are sometimes studied, convex ones are much more prevalent. Also there are only 36 questions tagged "polytopes" while there are hundreds tagged "convex polytopes."

EDIT: In light of comments below, I agree that it makes more sense to do the converse- have be a synonym of the more general or tag.

• Occurrences at this date: polytopes: 36; convex-polytopes: 608; polyhedra: 151. – YCor Feb 27 at 20:29
• One problem is that technically speaking, questions about non-convex polytopes do not fit in convex-polytopes. Other remark: it seems at first sight that most questions in polytopes are concerned with convex polytopes, and so do most in polyhedra. (...) – YCor Feb 27 at 20:34
• Hence, I would be inclined to make a single tag, named polyhedra for instance, or polytopes, or polyhedra-and-polytopes. With usage guidance, for instance "Polyhedra, polytopes, polyhedral cones, etc. Can be used in combination with convex-geometry. Convex polytopes are the convex hulls of a finite set of points in Euclidean spaces. They have rich combinatorial, arithmetic, and metrical theory, and are related to toric varieties and to linear programming." (The sentence in boldface is the current usage guidance for convex-geometry.) – YCor Feb 27 at 20:36
• I'm not sold on this. That a tag is little used is not a reason for it to be deleted. In this case, what is worth fixing is the confusing overlap. There are two approaches to fix this: put everything in the more general polytope, or create a new more specific tag about non-convex polytopes for the few questions that don't fit the convex polytope tag. I'd like to hear more about about what users of these tags think regarding these two options. – François G. Dorais Feb 27 at 23:20
• (Typo in my previous comment: the sentence in boldface is the current usage guidance for convex-polytopes, not for convex-geometry. Sorry for the additional noise.) – YCor Mar 2 at 15:46
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