# Tag management 2019

New year, new tag management thread.

Rules of the game are basically the same:

• A particularly bad tag (a rule of thumb: «if I can't imagine a person classifying a tag as either interesting or ignored, I'm getting rid of it»),
• A tag that should be a synonym of an existing one,
• A tag that used for two or more completely unrelated things,
• A need to create a new tag;
• Wait a couple of days before implementing a suggestion.
• After the problem described in an answer is resolved, please edit it to say so.

Also, note that one may use [tag:calculus] for , i.e. tags on the main site, and [meta-tag:discussion] for , i.e. for tags on the meta site.

Proposal to blacklist

Reason: It's overly broad and there is no real mathematical content in it. Also, the tag has been created and removed several times.

• As currently defined, it doesn't seem likely to be useful or consistently applied. It doesn't mean what I'd expect it to either, which would be something about dentifying different classes of theorem or proof and generic approaches to generalising ttem. So it's possibly a misleading tag too. – timtfj Jan 31 at 2:07

Resolved. All questions with have been retagged to (or neither tag, in a few cases where the tag was inappropriate) and will be automatically deleted soon

Apparently we have tags and , with 10 and 20 questions respectively (including 1 with both), different tag excerpts, and a tag wiki for the first one only. I don't know the topic very well, but the excerpts seem to describe essentially the same context. Should these tags be merged?

Resolved: renamed to .

For consistency with other multiple-word tags. Separating words with hyphens increases readability.

Resolved. The tags and have been renamed and , respectively.

Proposal: pluralize and

Putting names of mathematical objects in their plural form is a common practice, e.g. . We should treat "triangles" and "polygons" equally.

Resolved. has been renamed .

Proposal: rename "generalizedeigenvector" to "generalized-eigenvector"

Pledge originally initiated by WillG in this suggested tag wiki excerpt edit. I support this proposal since it's a common pratice to separate words with hyphens in tag names in order to increase readability, like , , , etc.

Resolved. is now .

Proposal: pluralize

Because… well, you know: there are two of them.

Partially resolved. has been synonymized into . A consensus has not yet been reached on the name change to .

Proposal: rename "topological-quantum-field-theory" to "topological-quantum-field-theories" and synonymise it with the tag "tqft"

An old question of mine recently had a couple of attempts to change the tags, which were approved (and I agree). In the process, the new tag was created, which I agree is better than the previous tag. However, a topological quantum field theory is a mathematical object like a group or a functor, and so the tag should be pluralised to distinguish it from a subject.

• Wait, theories? – Asaf Karagila Mar 7 at 14:04
• @AsafKaragila A topological quantum field theory is a functor from a cobordism category to a category of vector spaces (with some extra properties). There are many such functors, and so one usually wants to study them as a class of objects. – Dan Rust Mar 7 at 14:13
• There is already a separate post which is related to this: Some ideas on tags about physical field theory. I will add that creating a synonym between this tag and (tqft) seems like a reasonable idea. (So that both names are left in the system.) – Martin Sleziak Mar 7 at 14:14
• The first sentence made me cry from the inside, I have to admit. It's always a bit weird when your topic is the object. Group theorists don't study "group theories" per se, they study groups. And category theorists don't study "theories of category" per se, they study categories. Sure, you could argue that in fact we study the theories (is this consistent, does this imply that, etc.) but in reality we think about them in semantic terms. So it just surprises me every time when the "theory" part is the object, rather than the syntactic backbone of the object. – Asaf Karagila Mar 7 at 14:15
• @MartinSleziak thanks I hadn't seen that recent post (which explains why the recent edits were made). I agree that it should be a synonym, so I've edited this post. Asaf, I agree the naming convention is... unfortunate. I think this is a holdover from its history in physics. In fact it's possible that physicists may still study TQFT as a 'subject' rather than as an object. I'm not enough of an expert to comment on that. – Dan Rust Mar 7 at 14:46
• @Andrews I think the usage is different. A TQFT is an 'object' which is studied in mathematics as one member of a class of objects. A particular string theory is a sub-discipline of the subject-area 'string theory' and is not an 'object'. – Dan Rust Mar 7 at 16:00
• Still, "topological quantum field theory" as the subject seems to be widely used. For example, googling "topological quantum field theories" returns mostly articles titled "topological quantum field theory", some of which are written by reputable mathematicians (e.g. Aatiyah). Are you suggesting that the subject form is not used among mathematicians working on that subject? (What do they call it then?) – Alexander Gruber Mar 24 at 22:19
• @AlexanderGruber It's a good question and I don't feel close enough to give an answer. My limited exposure to TQFTs has always been as objects that are studied within category theory/low dimensional topology, but obviously there is a history in mathematical physics to consider. Atiyah's paper is maybe not the best reference point as it was literally the introduction of the definition and things have evolved greatly since then, such as Lurie's classification. Perhaps it's best to check which questions have already been tagged and try to work out which usage seems to be most prevalent. – Dan Rust Mar 25 at 0:24
• If someone with a bit more authority on TQFTs would like to offer their suggestion, that would also be useful. Alternatively, we could make a community wiki post and ask people to vote up/down for their preference. – Dan Rust Mar 25 at 0:24

Resolved: , , , and are now , , , and , respectively.

Proposal: pluralize , , , and .

(To match , , , , and , as well as the general philosophy of having things be plural.)

I'm actually not super convinced signed graphs are common enough to deserve their own tag, but if they are to have one it should be consistent with the other tags.

Resolved: has been merged into , a synonym created, and tag wiki updated.

Proposal: synonymize with

Notice that they are indeed different tags, as the former has user guidance, the latter doesn't. But they are essentially the same thing, i.e. a numerical method to solve first-order first-degree differential equations with a given initial value.

Resolved: The tag synonym was created.

I suggest a synonym $$\to$$ .

The tag (dg-algebras) was created in July 2017 (shortly before allowed length of tag names was increased). A short tag-excerpt was also created at the time. The tag (differential-graded-algebras) was created recently (July 2019).

It seems clear that both tags are intended for the same meaning. Hence they should be synonymized. (Probably the tag with full name might be more suitable for the master tag - although I'd guess that either way would be acceptable.)

I'll add that synonym between the tags with these names exists on MathOverflow.

Since the two tag names are probably due to change in the character limit for tag names, I'll add also a link to the thread about Expanding abbreviated tag names.

• Done as proposed. – quid Jul 7 at 19:18

Resolved. was removed.

Proposal: remove "continuoustime" tag

The tag has zero questions currently.

• If a tag has no question it dissappears after a day. There is no way for us to remove a tag "more" than having no more questions with it. (Note that the page would still exist, eg this-tag-does-not-exist.) – quid Feb 25 at 19:21
• To add to, here is an older post with a more detailed explanation: Deleting Tags after being created. – Martin Sleziak Feb 26 at 2:27

Resolved; and are created

Proposal : tag(s) for accessible and locally presentable categories

A couple months ago someone created (among others) the tags locally presentable categories and accessible categories, but they were removed. Now this is not really my specialty, but I think these tags could be useful, and in fact I was surprised to learn from Martin Sleziak that this was the first time they appeared.

Both topics give some search results on the site, and there seems to be no tag more precise than "category theory" on the questions about them. By the way, the tags exist on MO, and there are also a book and a lot of articles on the subject.

• I've created the tag for locally presentable categories; more info here – Arnaud D. Mar 26 at 23:12
• And now I've added the tag "accessible categories". – Arnaud D. Apr 20 at 8:31

Partially Resolved: is now , but the tag still lacks usage and a wiki.

Proposal: rename "singularvalues" to "singular-values"

There's no usage guidance and tag wiki yet.

Proposal to remove (or even blacklist)

It is a meta tag and it is a bad one. I sincerely ask the creator to stop retagging old questions until we have an actual discussion.

• As of now it has 0 tagged question. Let's hope they will stop now. – Arctic Char Jun 27 at 16:34
• For people who are unaware of the meaning of the phrase "meta tag" I will add a link to the relevant FAQ post: The “meta-tags”.. I'll also mention this question by the tag-creator: Relating to create a new tag. – Martin Sleziak Jun 29 at 3:43

Resolved (mostly) Creation of a tag . Merge of the GCD part, not yet merged the LCM part, in case some objection emerges. The tag wiki might need some (more) attention.

Proposal: merge and

We tend to combine homologus objects into one tag, like , and . It's well known that $$ab = \gcd(a,b) \times \mathrm{lcm}(a,b)$$, so knowing the implies the same for , and vice versa.

The majority of questions are also tagged with .

• A related previous post: On (gcd) and (greatest-common-divisor) and other similar tags. – Martin Sleziak Jun 14 at 13:09
• Maybe to gcd-and-lcm? – Alexander Gruber Aug 15 at 17:12
• @quid I just put a little bit of time into the tag wiki, but I am wondering if, perhaps, the tag info should be completely rewritten? Right now, it looks like a hodge-podge of facts about the gcd and lcm, without much in the way of guidance about how to use the tag. I'm not sure what would be better, but perhaps someone more intimate with these topics should have a look? – Xander Henderson Aug 31 at 14:31

Resolved: is now created.

Proposal: Create "mirror symmetry" tag

mirror symmetry is already a tag in MO, and there're already several questions about it now in MSE: (1), (2), (3), (4), (5).

Here is an introductory to mirror symmetry mathematically which says mirror symmetry introduces a correspondence between complex geometry and symplectic geometry, so actually it doesn't require strong physical background in string theory (physically).

I've already created and begin to add this tag to relevant questions gradually, and welcome to improve tag info and usage :)

• This is probably obvious, but the tag-info should clearly say what the tag is intended for. (Since many users when seeing the tag called mirror-symmetry will use it for problems related to reflections w.r.t. line/plane in geometry and not about the use in string theory, algebraic geometry and related areas.) So maybe it might be useful to suggest what the tag-excerpt and tag-wiki might look like. – Martin Sleziak Mar 23 at 10:47
• A way which could decrease the likelihood of such misuse of this new tag would be choosing a longer name which makes this distinction clear. (There are already a few such tags, for example, we have (lattice-orders) and (integer-lattices instead of just (lattices). Or (magma) and (magma-cas) to distinguish two different meanings of the word magma.) But I have to admit that I don't have a suggestion of a suitable name which would distinguish this tag from symmetry in geometry. – Martin Sleziak Mar 23 at 10:48
• Can you set up a more descriptive tag info? For example, please list several different aspects of the subject and for each cases, suggests some more suitable tags. (and mirror symmetry is not only about CY, at least they also study the mirror of some fano manifolds) – Arctic Char Mar 24 at 21:48
• @ArcticChar OK. And if you're familiar with mirror symmetry, you can help improve tag info, too. – Andrews Mar 25 at 7:03

Proposal: make a synonym of .

In theory, there is a distinction between these tags, with referring to just differentiable manifolds and also including topological manifolds. In practice, the distinction does not matter for many questions and alone is very frequently used for questions that are actually only about smooth manifolds. For example, looking at the 10 most recent questions, 8 of them seem to be primarily or entirely about smooth manifolds but only 3 of them are also tagged . If you want to use tags to signal that you are interested specifically in smooth manifolds, there are also other ways to do so, for instance using or .

• If the majority of "manifolds" questions seem to be about "smooth-manifolds", then maybe the synonym should go the other way around, and a separate tag "topological-manifolds" be introduced? – Willie Wong Jul 11 at 13:29
• Willie Wong's suggestion seems sensible to me. – Stella Biderman Sep 16 at 19:35

Proposal: create "linear-fractional-transformation", and synonymize with and .

They refer to the same thing in most basic cases.

Tag is really hard to notice its exsitence, and it only has 16 questions for almost 6 years.

• Isn't a linear fractional transformation more general? My understanding is that an LFT may be defined over any field, whereas a Möbius transformation is specifically an LFT over $\mathbb{C}$. This distinction may not require two distinct tags, but perhaps the tag "linear-fractional-transformation" should be created, with both lft and mobius-transformation being synonymized with that new tag? – Xander Henderson Apr 19 at 13:19
• Problem is I think many people asking about mobius transformations may not know the term linear fractional transformation, so that might be confusing to them. – Alexander Gruber Apr 29 at 0:54
• I would support renaming lft into linear-fractional-transformation, though – Alexander Gruber Apr 29 at 0:55

Resolved. is created.

Proposal: Create "semisimple-lie-algebras" tag

Semisimple lie algebras is an important class of Lie algebras, and we already have tag .

• I hope that I have not been presumptious, but there seems to be no objection to this tag, so I went ahead and created it – Xander Henderson Apr 19 at 13:15

Proposal: Create tag "squarefree" and its related tag info

I was surprised to find that we don't have a "squarefree" tag. There are about 350 Questions on Math.SE that mention "squarefree" (and about three times that many if all posts are included). Among other advantages, a tag would provide the wikia summary of basic ideas for this topic in number theory (or perhaps a bit more generally).

I have a dim memory of a discussion of "squarefree" vs. "quadratfrei" as terminology goes, but I can't find it on Meta Math (so maybe it was on a different site or newsgroup altogether).

Proposal: I suggest to create a synonym between and . (I am not really sure which direction is better.)

The tag has been on the site for some time, you can see that the tag-excerpt and the tag-wiki have been created in 2013. The tag has been created recently (July 2019).

As far as I can tell, the two names are often used as synonyms. Even the tag-excerpt for (linear-groups) says that: "A linear group or matrix group is a group $$G$$ whose elements are invertible $$n \times n$$ matrices over a field $$F$$."

It's possible that sometimes people make distinction between the two terms. The Wikipedia article Linear group says: "In mathematics, a matrix group is a group G consisting of invertible matrices over a specified field K, with the operation of matrix multiplication, and a linear group is an abstract group that is isomorphic to a matrix group over a field K, in other words, admitting a faithful, finite-dimensional representation over K." However, from the tag-info I gather that the intended usage of the tag (linear-groups) was for groups of matrices.

Since both names are used, I suppose that having a synonym might be useful. (A user posting a question will be able to find the tag both if they starts typing "matrix" and if they start typing "linear".)

Partially Resolved: created. We still need a tag wiki and adding the tag to a few old questions.

Proposal: create tag "stochastic-programming"

Reason:

1. It's an area of research.
2. There's over a hundred stochastic programming questions.

Proposal: Tag suggestion:

Resolved: the tag is removed from that one question.

Please consider removing the tag 4d. It is a new tag and has only one question, which is about cube in 4d.

On one hand, it is definitely not necessary to have the tag $$nd$$ for all $$n\in \mathbb N$$. More importantly, four dimensional manifold has a special role in differential geometry, so the tag $$4d$$, if it remains, might eventually contains a mixture of questions in elementary geometry and (very advanced) differential geometry.

I have tried to remove the tags but some other disagree.

Following an earlier discussion I approved a synonym to . Likely down the road a merge will happen.

The main reasons are:

• we do not separate tags by level, and in this case there even is that is an "advanced" tag so that further separation seems not useful.

• the community did over the past two years not use that tag much. In absolute numbers usage is not that bad (about 70), but there are thousand times as many question in overall. Thus, one could say, it is basically just not used at all.

Proposal : create to differentiate from .

The tag currently has 18 questions, 12 of which are about the Grothendieck group rather than the Grothendieck construction (there is no tag-wiki). A search for "Grothendieck construction" (without the quotation marks) returns 70 questions, and there seem to be questions about both concepts that do not have the tag.

Since the two concepts are, as far as I know, unrelated, this seems to be a misuse of the tag. I would therefore suggest to create (or maybe a less ambiguous name, such as would be even better) and retag the questions as necessary.

• I upvoted, but I am specifically in favor of creating the tag group-completion. Such a tag title seems more descriptive than "Grothendieck group". – Xander Henderson Sep 16 at 23:25
• I think there is a dire need for a tag wiki here. I'm somewhat ignorant, but for me Grothendieck group only means the group you get from an abelian category by modding out short exact sequences. Similarly, to me the phrase group completion would trigger an expectation of seeing questions related to profinite groups and such. In other words, I might unwittingly tag/retag questions here without a tag wiki. – Jyrki Lahtonen Oct 27 at 12:14

Proposal: pluralise .

Reasons:

1. It's a convention to have pluralised tag names if possible.
2. A proposition sometimes has multiple proofs.

Should we have a tag?

We have quite a few related questions that are currently spread across different nearby tags (such as , , and ) but no one tag to unite them.

• Here is a similar search restricted to questions, it gives 158 results at the moment. BTW I have asked Michael Greinecker about this tag proposal in chat, so far I got no response. – Martin Sleziak Aug 18 at 6:58

Proposal: I think there is no requirement to place the new tag named simplex-method, which has been created by an user few days ago and already $$2$$ questions are added here. Since there is already a tag named linear-programming and this contains many methods like the simplex method, dual-simplex-method, graphical method etc. etc..

I want a suitable opinion about my proposal.

Thank you.

• I will add that the tag was created a few days ago, on August 31. It seems that some questions about the simplex method are tagged simplex+linear-programming. I will point out that there also is a separate tag (two-phase-simplex) for the the two phase simplex method. – Martin Sleziak Sep 6 at 8:12
• So what you think, is it alright ? – nmasanta Sep 6 at 8:33
• Actually, I would probably a bit more in favor of the tag. (I have mentioned possibility of creating this tag in chat quite a long time ago but I got no response - so it's good that you brought this up on meta, it's more likely that this gets some feedback here.) It would be good to hear from the people who are active in the (linear-programming) tag, they are in the best position to judge whether this tag might be useful.. – Martin Sleziak Sep 6 at 8:40
• Yes, I agree with you. Let's see what the others say. – nmasanta Sep 6 at 8:43

Proposal: rename the synonym "laplaces-equation" to "laplace-equation" or to ''laplace's-equation''.

laplaces-equationis a synonym of harmonic-functions.

I think we should have remove the s from laplaces-equation or give an Apostrophe before s (i.e., 's) .

There is nothing called laplaces-equation rather we can called it laplace's-equation or simply "laplace-equation".

Want suitable opinion about my proposal.

• I think that putting an apostrophe is not possible for technical reasons. Let me try : if we type [tag:laplace's-equation] we get as a result [tag:laplace's-equation], but if instead we type [tag:laplaces-equation] we get as a result laplaces-equation. – Arnaud D. Sep 11 at 8:12
• I've also tried creating a tag with an apostrophe in the name, and it was treated as two words. So laplace's-equation seems impossible to create. Maybe laplace-equation would be better, but I'm not sure it's really worth changing a tag that's only a synonym anyway... – Arnaud D. Sep 11 at 8:17
• Sorry @Arnaud D. ~~I just proposed to rename the phrase, not to create any tag. – nmasanta Sep 11 at 8:19
• But the problem is the same : you can't have apostrophes in tag names (as far as I know) so we can't rename the tag with laplace's-equation. – Arnaud D. Sep 11 at 8:25
• Okay, if so, then we can rename it as laplace-equation. I think it doesn't make sense to have one extra character s. – nmasanta Sep 11 at 8:30