# Tag merging and synonyms [closed]

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.

• Changes are automatically recorded at math.stackexchange.com/tags/synonyms?filter=all&tab=master , 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: meta.math.stackexchange.com/q/12485 – Grigory M Jan 16 '14 at 16:08
• This question is now superseded by the Winter tag cleanup thread. – user642796 Feb 6 '14 at 9:08

Do we really need around? While at it, seems a bit redundant too.

Lastly, seems like it could be renamed to be except perhaps a small handful which can be easily corrected manually.

• The (transformation) tag is an extremely bad one. Not all of the items in it are linear-transformations, it will require sorting through by hand. Someone seems to have dealt with mapping. I am not sure about (parity). It is a valid, named concept in mathematics. But with only 4 questions in it, it is not looking like it is too useful. – Willie Wong Jul 22 '11 at 21:31
• @Willie: My sentiments exactly. – Asaf Karagila Jul 22 '11 at 21:54
• Oops, (mapping) was not dealt with. There seems to have been a glitch the last time I checked, because now it looks like it has 9 question. – Willie Wong Jul 23 '11 at 0:23
• @Willie: It seems that just as you finished with (mappings) it came back, along with its brother (hash-function), both seem out of place (to the site, not to the question). – Asaf Karagila Jul 23 '11 at 18:09
• You could have just dealt with mappings too. You know. OTOH, I've never dealt with hash-function. Since non-research-level theoretical computer science is technically on topic, I don't think we should do anything about hash-function. – Willie Wong Jul 23 '11 at 19:24
• @Willie: Just removing seems bland and tasteless, I was unsure what to do. I figured I could either ping you here, or flag the post which would probably be a bad idea... – Asaf Karagila Jul 23 '11 at 20:33

Edit: I think that the conclusion is that we should keep this tag.

Is there a need for a tag? Currently there are two questions under it, but knowing the various generalities in which one can consider tensor products suggest that this tag may accumulate a lot of questions with different assumptions.

It would be good if users remember to also tag with an appropriate subject tag to help clarify. Maybe a reminder is in order in the Tag Wiki?

• Actually, why not? I think tensor products are among the most difficult things one encounters in linear algebra (or wherever one sees them first) and tagging a few more questions thus may be really helpful for some. (but maybe I misunderstand the purpose of tagging yet again). By the way there are now seven questions and all tagged this way by the OP except for one that you retagged from tensors. – t.b. Aug 1 '11 at 2:35
• @Theo: I was not sure tensor products should refer to linear/multilinear algebra (or functional analysis), or modules/rings, or vector bundles, or monoidal categories, or maybe all? Perhaps we should specify in the wiki that one should also tag appropriately depending on which subject in which one encounters the tensor product? – Willie Wong Aug 1 '11 at 10:38
• I wrote a first version of a possible tag wiki excerpt. – t.b. Aug 1 '11 at 11:07
• @Theo: looks good. I edited it slightly to include a one-line blurb about what tensor products are (to fit the space constraint I used the universal property version). I think we can keep this tag then. – Willie Wong Aug 1 '11 at 11:38
• Very good, I didn't see how to fit that in... I suggested some commas. – t.b. Aug 1 '11 at 11:43
• I just observed that we have (tensors) and (tensor-products) now. What do you think about this? While tensors are probably a thing I missed in the tag-wiki it will not be obvious to all users how tensors (you know what I mean: $R_{ijkl}$ and pals) relate to tensor products. Should we make a synonym or keep a special tag for these index-laden beasts? – t.b. Aug 1 '11 at 15:58
• @Theo: I think the two should be two separate tags. But some of the questions in (tensors) should be retagged to (tensor-products). I am thinking that there would be some more applied-oriented questions where tensors are defined as "higher rank vectors with certain transformation properties under coordinate changes". – Willie Wong Aug 1 '11 at 16:08
• That's exactly what I meant to say. I'll go and re-tag some of them now, okay? – t.b. Aug 1 '11 at 16:12
• @Theo Thanks. There are around 12 or so, I think? I've also written a blurb for the exerpt, please see if it can be improved. – Willie Wong Aug 1 '11 at 16:15
• I read your tag wiki and I like it. I think with the one question you just caught the tagging seems to be consistent on both sides now. Can you somehow squeeze in a cross-reference back to (tensors) in the (tensor-products) wiki? But maybe it's not necessary. – t.b. Aug 1 '11 at 16:42

In the comments thread to this answer the question came up what to do with the rather ugly . I don't like that tag very much, as it seems to me that it should be split up into and .

From a quick glance on the manifold-questions, I think the least intrusive way to do it is:

1. retag those questions that are not
2. merge into .

No, should not be merged into : 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".

Still I don't understand why one needs three tags: , , .

• While I don't like the tag (manifold) too, I don't really think that just using smooth manifold makes a question (differential-geometry) — like, you know, most of the questions with numbers are not (number-theory). So we'll have to manually retag most of these questions, I'm afraid. – Grigory M Aug 18 '11 at 12:34
• Actually, that comment you cited was mostly to "educate" :) Asaf. While I agree that manifold is an ugly tag, to properly divvy it up we need to probably split it into (smooth-manifolds) (topological-manifolds) and (PL-manifolds). Also, I've always been a bit puzzled by the (differential-geometry) vs (differential-topology) distinction. While I know well that there is a strong distinction at the deeper levels (connections, vector bundles, and what nots), most of the elementary questions about the two subjects asked on this site can equally well fit into either. – Willie Wong Aug 18 '11 at 12:38
• @Willie I'd say (differential-geometry) is when one uses some metrical properties (hence connections, curvature and so on). – Grigory M Aug 18 '11 at 12:43
• @Grigory: right. Ryan Budney seems to agree – t.b. Aug 18 '11 at 12:44
• @Grigory and Theo: in the abstract, I agree. But this distinction is going to be hard to explain to a 3rd year undergrad who has taken only a first course in differential geometry, which at various universities may mean actually differential topology, differential geometry, or even Riemannian geometry. (To put it differently: I perfectly understand and appreciate the distinction of the two subjects. I am just not optimistic that the two distinct tags would be used properly.) – Willie Wong Aug 18 '11 at 13:00
• @Willie: Okay, I can live with that and I see the problem. But: can we please rename (manifold) into (manifolds)? – t.b. Aug 18 '11 at 13:02
• @Theo: I didn't do that already? Shame on me! It must've gotten lost in the queue. – Willie Wong Aug 18 '11 at 13:05
• @Willie (re: not optimistic) Probably you're right, but (editing) tag wikis could help a little... – Grigory M Aug 18 '11 at 13:58
• @Grigory I agree. Ideally if Ryan Budney (or someone with a better idea of what precisely differential topology is about) would be so kind to write the (differential-topology) wiki. The (differential-geometry) one looks okay. – Willie Wong Aug 18 '11 at 14:57

From the recently opened tags, there are several tags whose usefulness is unclear. I'm posting this short list here because I see no reason to start a full thread about it, but I am also listing all the tags at once because there is quite a few of them.

If you remove some of the tags, please strike them off the list (or mark them somehow to signify that you've done so.)

1. (foundations)
2. $\checkmark$ (judging by Willie's retagging it seems this one is a keeper)
3. $\leftarrow$ Someone please look into this one, the tag itself is growing and it is better to mass-retag when there are only five questions, not when there are 20.
4. (pseudonoise)
5. (lfsr)

On that list it is possible that quivers deserve their own tag, and the question whether or not we want a tag for general foundations questions is also open. I also think that is a bad tag because we already had problems with recursion related tag names and there was quite an agreement that those are unclear.

Lastly, I think that we should all agree that tags should be at least a bit meaningful. So should probably be renamed if not removed.

• Hmm, ideally, rubiks-cube should be under recreational-mathematics, but it does seem that we have already a number of Rubik questions that maybe a separate tag is justifiable... – J. M. is a poor mathematician Apr 18 '12 at 13:09
• On that note: should the time come that we suddenly have a lot of questions on linear feedback shift registers, I'd not be surprised why some might want to use the acronym instead... – J. M. is a poor mathematician Apr 18 '12 at 13:12
• @J.M.: You crossed off [lfsr] but there are still three questions tagged. Do you intend to retag them, or just think that the tag should stay? – Asaf Karagila Apr 18 '12 at 13:17
• Hit too early. Ought to be okay now... – J. M. is a poor mathematician Apr 18 '12 at 13:24
• Seeing that there are +10 questions specifically about Rubiks cubes, it may be worth keeping. (Up until recently I was with JM in thinking that it should be recreational-maths, but the number has gone up a bit in the past month or so; granted some of them are not the best of questions. At the very least it will help people search for duplicates.) – Willie Wong Apr 26 '12 at 13:30
• Note that also some of the "possibly useful" (in the sense of describing a mathematical concept) tags can be left alone: if after 6 months there aren't much usage, the orphaned tags will be automatically cleaned up. If usage goes up, well, maybe they could stay. – Willie Wong Apr 26 '12 at 13:49
• @Willie: Single question means orphaned tag? – Asaf Karagila Apr 26 '12 at 13:53
• Maybe it is not the best terminology, but Jeff uses it here so I do too. – Willie Wong Apr 26 '12 at 13:56
• @Willie: Ah, I see. [recursion] and [fractional-calculus] are both with more than one question each. The former is troublesome in light of previous discussions about recursion named tags being ambiguous; the latter... I just don't know about. – Asaf Karagila Apr 26 '12 at 14:02
• I think [fractional-calculus] may deserve to stay. [recursion] however, is a can of worms. It'd be great if we can get Henning or someone else more familiar with the subject to comment on it. – Willie Wong Apr 26 '12 at 14:13
• I don't know; fractional calculus is interesting, but not terribly popular. But there is no way of telling if we might get a torrent of differintegral questions tomorrow, after all... – J. M. is a poor mathematician Apr 26 '12 at 14:13
• @Willie: my feelings about recursion aren't too different from my feelings for inverse; somewhat overloaded that maybe it's not a very good tag to have. – J. M. is a poor mathematician Apr 26 '12 at 14:15
• @J.M.: I ran a search on torrent search engines, and it seems unlikely we'll find one tomorrow... :-P could you alert Henning to this thread and fill him in on the recursion issue? It seems we'll all benefit from his advice here. – Asaf Karagila Apr 26 '12 at 14:15
• I like (quiver) in the sense that I'd have nothing against a (quivers) tag and there's a bunch of questions that could be tagged this way. Points 1-4 could use deletion and 5 is at least debatable. Fractional calculus shows up occasionally. – t.b. May 7 '12 at 11:18
• @Henning: I do not know if we can make a pseudo-tag. The closest (that I know of) we can do is to make [recursion] a synonym of [recurrence-relations] and rely on people to retag with that tag is not appropriate. – Willie Wong Jun 19 '12 at 12:16

It seems that most questions on hopf algebras are tagged . Today the tag was created (in this question). Should these two tags by synonyms?

As I know nothing about these two notions, I hope someone more familiar with them could be able to tell what is correct thing to do.

• Even though the most common occurrence of Hopf algebra problems will be from quantum groups, they also turn up in the study of algebraic groups and to some extend of Lie algebras (via the universal enveloping algebra), and as such, the tags are not quite synonyms. – Tobias Kildetoft Jul 16 '12 at 13:33
• Based on Tobias comment, keeping the tag seems to be reasonable. I've added one more question to hopf-algebras to avoid automatic removal (the tags containing only one question are removed after 6 months). I'll leave the activity related to this tag for people who know more about this area. – Martin Sleziak Jul 17 '12 at 10:33

Resolved: no longer exists: may it rot in hell rest in pieces peace.

A recently created tag should probably be deleted before someone uses it.

• A tag with no questions associated with it will be automatically deleted. In fact, miscellaneous has already been deleted from the system. Tag-links (such as I edited into the answer, and the one in the previous sentence) always goes somewhere, even nonsense tags like untendablestuffman which clearly don't exist... yet. – user642796 Jan 17 '14 at 16:15

Why do we have both and ?

• simplex should go away, but not all those problems belong under "simplicial-". Problems involving simplex method should be tagged optimization; integration over a simplex belongs under multivariable-calculus and integration. By the way, there ought to be a better tag name than -stuff; maybe simplicial-objects? – Post No Bulls Dec 7 '13 at 16:02
• @PostNoBills: why should (simplex) go away? Simplices are perfectly normal mathematical objects. The (simplicial-stuff) has some history. – Willie Wong Dec 9 '13 at 10:20
• @Willie: I thought that the main stuff in simplicial stuff was simplices... – Asaf Karagila Dec 9 '13 at 10:22
• @AsafKaragila: evidently not, at least from what I can glean from the discussion on that thread. – Willie Wong Dec 9 '13 at 10:24
• @Willie: Well, at least in theory... In that case, what do we need the simplex tag for? – Asaf Karagila Dec 9 '13 at 10:38
• @AsafKaragila perhaps for questions about actual simplices? There are some nice and elementary geometry stuff about simplices which are not as highfaluting as the stuff usually considered "simplicial stuff". – Willie Wong Dec 9 '13 at 11:14
• Tag wiki for 'simplicial-stuff' explicitly asks 'Please do not use for questions about geometry of simplices nor about triangulations'. – Grigory M Jan 6 '14 at 17:37

While writing up a question, I found and , with more favored. I'd recommend a tag synonym.

• I vote against this merge. I just think that the two tags should remain separate. – Asaf Karagila Jun 23 '11 at 15:45
• @Asaf: Could you explain on what grounds, so I can understand your reasoning? – Michael Chen Jun 23 '11 at 15:47
• @Michael: I just think that there is a distinction between questions about terminology and questions about definitions. – Asaf Karagila Jun 23 '11 at 15:51
• @Asaf: I think to most questioners and answerers, the distinction is not that wide. I see some questions in terminology that ask about the meanings of words, and I also see questions in definition that ask about the name of such-and-such. At the core, they are both about meanings. – Michael Chen Jun 23 '11 at 15:57
• @Michael: By that logic one could say that all questions should be tagged under set-theory (and sadly, many newcomers do that for no apparent reason). Terminology and definitions are dual notions, in the former you ask about the names for a given definition while in the latter you ask about the definition of a given name. – Asaf Karagila Jun 23 '11 at 16:24
• @Asaf: Do you see a situation where a questioner/answerer is looking for one to the exclusion of the other? I myself am unable to see a case where you'd like to search for one and not the other. I dislike appealing to definitions (pun not intended), but the tag wiki for terminology implies that it is also where you would ask definition-based questions. – Michael Chen Jun 23 '11 at 18:46
• @Asaf and @Michael : perversely I agree with Asaf that there is a subtle distinction between terminology and definition. However, I won't go so far to say that they shouldn't be synonyms for tagging purposes--the distinction is rather subtle, and the constant retagging of questions from one to the other may not be worth the effort. Instead of "duking it out" here in the comment threads though, may I suggest one of you start a new Meta.Math topic on this? Clearly there is some contention to whether this change should be implemented or not, so it is better if we discuss it in public. – Willie Wong Jun 24 '11 at 0:52
• @Willie: Very well, however in the next day or so I will be mostly incapacitated to answer, so I will have to ask and wait for me to recover from today's wonders before making a decision. Also, perversely?? :-P – Asaf Karagila Jun 24 '11 at 6:46
• @Asaf: as you probably correctly surmised, that adverb applies to the "I agree with Asaf" part and not to the part about existence of subtle distinction. :-) – Willie Wong Jun 24 '11 at 12:49
• @Willie: That is a good idea, and I will do as you suggest. – Michael Chen Jun 26 '11 at 3:44
• @Asaf: When you're ready in the next day or so, do you want to post to meta.math? I'm thinking we make it community wiki and have a pro answer and a con answer, which people can choose via upvote (but ignore downvotes). – Michael Chen Jun 26 '11 at 3:46
• @Michael: I will post a question, you can write the pro merge, I will write the con merge. No actual need for CW since this is meta anyway. – Asaf Karagila Jun 26 '11 at 6:36
• @Willie, Michael: meta.math.stackexchange.com/questions/825/… might be relevant and not require any new thread? – Asaf Karagila Jun 26 '11 at 8:28
• @Asaf: Can the question be revived easily? – Michael Chen Jun 26 '11 at 23:47
• @Michael: I don't know any other way than checking. Just posting an answer or edit should do the trick. – Asaf Karagila Jun 27 '11 at 8:25

Can we please delete . This is a subjective tag.

• I don't think so. There are legitimate on-topic questions about how to write/present proofs which are more or less independent of what the proof happens to be about. – Henning Makholm Mar 4 '12 at 4:39
• @HenningMakholm: How to write/present proofs is a bit subjective, isn't it? All we get it someone's opinion about some very (likely) localized problem (from what few questions I saw). Can you please point me to some question for which the proof-writing tag is necessary and which might be not be too localized? Note: I am just trying to understand why the tag is there, I might end up agreeing with you :-) – Aryabhata Mar 4 '12 at 7:11

I propose the following tag synonyms:

1. $\leftarrow$ , because the topics seem related enough and all but one of five questions in the latter share the first as well.
2. (elementary-number-theory) $\leftarrow$ (divisibility), because also divisibility appears in the tag wiki of the first.
3. (combinatorics) $\leftarrow$ (combinatorial-designs), all questions from the latter tag share the first as well.
• Synonym is not a synonym of subset. The tag synonym system is for when two tags refer to the same concept. Even if every conditional probability question is a probability question, not every probability question is a conditional probability question. – Rahul Mar 4 '13 at 8:22
• @RahulNarain ok, then please vote down the corresponding tag synonym proposal, if you think we need both tags...What about the others? – draks ... Mar 4 '13 at 8:32
• What about the others? Do you think every elementary number theory question is a divisibility question, and every combinatorics question is a combinatorial designs question? – Rahul Mar 4 '13 at 8:39
• No the other way. Maybe I got the concept wrong...but why is counting (primes for example) synonym to combinatorics? – draks ... Mar 4 '13 at 9:04
• @draks: about counting, that is because for the most part when the synonym was proposed, the questions tagged "counting" were mostly about "count how many cases" which is by definition combinatorics. – Willie Wong Mar 5 '13 at 11:47
• @Rahul: I think the fact that there is a master and a slave tag in the synonym system means that we don't have to be so strictly observant of the $A\subset B$ and $B\subset A$ rule. By draks' proposal anytime someone tags (divisibility) the question would be retagged (elementary-number-theory), and not the other way around, so I don't really think you objection is that serious. – Willie Wong Mar 5 '13 at 11:50
• @Willie: That makes it impossible to indicate that a question is about combinatorial designs, or about divisibility. Is that desirable? – Rahul Mar 5 '13 at 12:13
• @Rahul: that was a general comment saying that just because $A$ is a strict subset of $B$ should not prevent a synonym from being created from $A\to B$. See for example JM's proposal below of "(trigonometric-identities) -> (trigonometry)" which got approved by user votes. (You have 10K, so you can see it.) Whether a tag should stand should be judged by other factors than just "it is not exactly the same as an existing tag". – Willie Wong Mar 5 '13 at 13:46
• @Rahul: my opinion is that the (combinatorial-designs) tag should stay, while (divisibility) should go. But as my votes are binding and there's no universal agreement, I'll refrain from casting a vote either way. (conditional-probability) could probably stay for now to be revisited later. I'm not convinced either way. Lastly, tag synonyms can be undone, as has happened with (physics) and (mathematical-physics). (Though sometimes it requires a little bit of retagging afterward to sort through the changes.) – Willie Wong Mar 5 '13 at 13:48
• @Willie: OK, I take back my objection to (divisibility). And (conditional-probability) seems like a pretty useless tag; I wonder if we shouldn't just delete it instead of making it a synonym. I guess I overreacted to the fact that the only rationale given for the suggested synonyms was that they were subsets of another tag. – Rahul Mar 5 '13 at 15:05
• Deleting the tag (conditional-probability) was a most unwise decision (whose rationalizations above do not hold water and make for a rather odd reading). People, just grab any modern probability theory textbook and tick the chapters in it on this very subject... Was the deletion acted upon by two users in all, if I read correctly? – Did Mar 8 '17 at 7:32
• I will add that there is a new post about the synonym between (conditional-probability) and (probability) in the 2018 thread: math.meta.stackexchange.com/questions/27653/… – Martin Sleziak Jul 28 '18 at 13:56