New year, new tag management thread.

Rules of the game are basically the same:

  • Post your suggestion as an answer here if you see
    • 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;
  • Upvote/downvote/comment as your agree/disagree with suggestions, so please post different suggestions in separate answers;
  • Wait a couple of days before implementing a suggestion.
  • After the problem described in an answer is resolved, please edit it to say so.
  • If your tag suggestion exists in a separate question, please provide a link to the question in your suggestion.

See also:

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.

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    You might want to make a comment as I did of the topics that are still open. – suomynonA Jan 9 at 5:07
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    @suomynonA Thanks, I'll work on that sometime this week. – Clarinetist Jan 9 at 14:10
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    That's a long week. :) – Asaf Karagila Mar 25 at 10:00
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    @AsafKaragila Thanks for pinging me! It's done now! :) – Clarinetist Mar 25 at 16:23

20 Answers 20

Given the recent meta question about the tag "functions" is more than one month's old. I suggest we implement the most up-voted action: to rename the tag.

If I understand correctly (here), renaming can be done either by merging or setting up a tag synonyms. In any case, one has to have another tag to start with. Thus I suggest introducing the mapping tag as follows:

(Name): Mapping


For questions about basic (set-theoretic) properties of a mapping $f: A\to B$ between two sets $A, B$.


A mapping $f$ from $A$ to $B$ is roughly speaking an assignment, for each element $a$ in $A$, an unique element $f(a)$ in $B$. A mapping is also commonly called a function. Mapping is one of the most fundamental concepts in mathematics.

Any question concerning the most basic properties of mappings should use this tag. This includes:

  • Basic notations,

  • Domain, codomain, image, preimage of a mapping.

Depending on context, please consider also adding algebra-precalculus or elementary-set-theory. Do not use this tag simply because it has a function in the question.

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    Perhaps "Do not use this tag simply because it has a function in the question" should also go in the excerpt, so that a few more users will notice the instruction. – Misha Lavrov Mar 26 at 1:58
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    @Misha: Although a good idea, we have sort of "reverse survivor bias" (so, casualty bias?) in the sense that we have no idea how effective these messages are. We only see the masses which ignore them entirely in play. – Asaf Karagila Mar 26 at 11:34

I've noticed we have both and . Would it make sense to make the former an alias of the latter?

  • And jacobi-symbol is out there too. I don’t know why, but my gut feeling is that there is room for all of these. But, maybe I’m in the minority. – pjs36 Apr 11 at 21:37
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    There are now synonym suggestions (jacobi-symbol) $\to$ (quadratic-residues) and (legendre-symbol) $\to$ (quadratic-residues). (One of them was suggested by barto, the other one by me.) Users with sufficient score in the tag can vote for/against them here. Maybe it could be useful to include this information into your post - that could attract attention of users who might vote on those synonyms. (And perhaps attract also some users who have something to add to this discussion.) – Martin Sleziak May 29 at 6:24

2017 Outstanding Tag Management:

2016 Outstanding Tag Management:

Proposal to rename to (quadratic-equations)

Reason: Mathematical objects in tag names have plural forms, say , , , etc

Proposal to pluralize and to make a synonym of "reproducing-kernel-hilbert-spaces"


  1. Idem to my previous proposal: we have .
  2. RKHS is a widely-accepted acronym for .
  3. Short acronyms are good for tag names, e.g. , and . Unlike and , doesn't even have a tag synonym "stochastic-differential-equations". (I support the creation of such synonym though.)

I suggest to rename to . (Now that the limit for the length of tagnames is 35 characters, the latter is a possible name for a tag.)

Both the tag-excerpt and the tag-info for (differential-equations) explicitly say that it is for ODEs and not for PDEs. And there is also a synonym with the tag . Here is the current revision of the tag-excerpt:

Questions on (ordinary) differential equations. For questions specifically concerning partial differential equations, use the (pde) tag.

This tag is also among the suggestions for tag-warnings: Do we want tag warnings, and for which tags?

As far as I can tell, there are enough experienced users here who know that this tag is only for ODEs and who retag the questions which are incorrectly tagged. But perhaps if the purpose of the tag is clear already from the tag name, then the likelihood of askers tagging their questions incorrectly would be a bit smaller.

I'm not sure that the tag is needed. Julia sets lie squarely in the realm of complex dynamics, which averages only a few questions a month. The tag was introduced very recently and contained just one question. I edited the question to be tagged instead.


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    It is not clear from this post whether you have some proposal about this tag. If you are saying that the tag should be removed, then this was achieved. If you want to suggest a synonym, then you should mention which tag you consider as a suitable master tag. – Martin Sleziak Jul 12 at 8:06

I noticed that a new tag has been created this year, apparently in February. I first noticed it today, while reviewing a suggested tag-wiki for the tag.

I do not think the coincidences tag is necessary, nor helpful. If users could add up to ten tags on any question, then perhaps it doesn't hurt to have it. But at this point in time, the maximum tags for any questions is five.

Only 17 questions on MSE have the "coincidences" tag.

Proposal to eliminate the tag

This tag has no usage guidance and it was used so far for a single question. I suggest that we eliminate it.

Suggestion: Rename tag to box-topology.

The tag is of low usage (fewer than a dozen instances, some of which are inappropriate if the proper application is for topology. I noticed this tag in reviewing a tag wiki excerpt which presumed that was the intention, but I rejected it as being nearly of the form [tag] is for questions about [tag].

So an alternative that I could live with is to delete the tag.

Resolved: has been created. Synonyms include and .

We need a tag for topological data analysis.

It is a rapidly growing field, so there will be more and more posts about it. Currently, questions about TDA come up under the tags , , , , and a few more. These are insufficient for searchability as TDA is its own distinct topic that is not directly encompassed by any of these tags.

We have a few options here.

I'd like some feedback on which of these would be the best choice, which (if any) should be synonyms, and whether there is a better name for the tag that I haven't thought of.

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    I'd go with the [topological-data-anaylsis] tag, it's the most descriptive for people outside the field. And in any case, not [persistence]. You'd end up cleaning this from users who had a persistent problem... – Asaf Karagila Jul 29 at 15:52
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    To second @AsafKaragila's comment, I think that it is useful to have a tag that cannot be easily misunderstood. [persistence] and [computational-topology] both seem like they could be easily misunderstood by a newbie (i.e. how do I compute the fundamental group of some topological space). I think that [topological-data-analysis] is the best choice, with (perhaps) [persistent-topology] as a synonym. – Xander Henderson Jul 29 at 19:41

I have noticed that there is a tag named on meta. It is actually one of the default tags - these are the tags that are automatically created on every new meta site and are not deleted even if they have zero questions.

You may notice that on Meta Stack Exchange, this tag is now a synonym of (favorite-tags). And I'd guess most users know this feature under the name favorite tags. (Maybe it was called differently at the time when the default tags were selected.) I think that average user would have hard time guessing what (interesting-tags) is intended for. Which might lead to inconsistent usage of this tag and some incorrectly tagged questions.

My suggestion is to clarify usage of this tag and also make the name correspond to today's terminology.

  • One possibility would be to create a new tag and make this tag a synonym. (With (favorite-tags) as the master tag. This would basically copy the usage on Meta Stack Exchange.)
  • Another option would be to create a tag synonym $\to$ and use (favorites) both for favorite questions and favorite tags.

If you look at current usage of the tag and also if you check current revision of the tag-excerpt and the tag-wiki, you can see that this tag is currently used for both favorite tags and favorite question. (I am partly to blame - I have used the tag in this way and also I have created the tag-info. However, at the time it seemed to me a bit redundant to create a separate tag for favorite tags.)

This means that if we decide to have a separate tag for , this would require also retagging of a few older questions. Which is why I am inclined more to the latter option, i.e., to have one tag for both favorite tags and favorite question.

But I am certainly open to the other solution. We can discuss (and vote) in comments which of the two options is better.

Rename to

The outcome of Revisiting the "partitions" tag was the splitting of by the creation of new tags and . The question also proposed that be renamed to , and the consensus (and only) answer proposed to do this at the end of the retagging process. However, the retagging was completed months ago, the rename is still outstanding, and it's still frequently necessary to fix new questions which have been incorrectly tagged instead of (or in addition to) or .

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    Done. I am not sure why I did not react on your comment in April; as I have no memory of having seen it, I likely just missed it. Sorry for the delay. – quid Jun 29 at 21:42

Resolved (the synonym is no more)

The tag has been deleted/subsumed/transformed into the tag roughly five years ago, thus making impossible to signal as such, questions involving conditional probabilities conditioned by a sigma-algebra in the general case, and in particular conditional probabilities conditioned by a continuous random variable. This inappropriate decision should be undone.

If I am reading this post correctly, the deletion of was decided and enacted by a small number of users with no noticeable activity in the subject. Oddly, and fortunately, the tag survived.

Resolved: has been renamed to .

There is an ongoing discussion on at The tag even-and-odd-extensions.

Proposal to pluralize sequence-of-function

I have some doubts about the existence of a sequence-of-function tag. But, since it exists, I propose that its name becomes sequence-of-functions instead.

  • Merely as a historical curiosity, I will mention that the tag (sequence-of-functions) was created in January 2015 and later removed. The new tag (sequence-of-function) was created in May 2017 and still exists. (See the related comments in the tagging chatroom for more details.) – Martin Sleziak Aug 29 at 11:18
  • @MartinSleziak That's interesting. I was not aware of that. – José Carlos Santos Aug 29 at 11:45

As recently pointed on this thread, we are going to get rid of . Today I noticed that we also have .

I feel that this tag can go just as well as part of the process.

I suggest eliminating the tag .

Someone just this tag today, and added it to three questions. As written, the description is... the most generic thing ever, basically "anything associated with permutation groups and permutation cycles". Given that there is already a tag, what purpose does the (permutation-cycles) tag add?

(As a side note, why is the tag a synonym for (permutations)? There are lots of cases where people are dealing with problems involving permutations, but not working with a group. Likewise, there are a lot of interesting group theory problems about permutation actions that are not covered by other tags.)

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    permutation-cycles may, in theory, be a good tag for searchability purposes. Decomposing a permutation into cycles is a common topic in elementary group theory courses and those problems show up enough in permutations to warrant their own tag, if only to exclude that type of problem during a search – Alexander Gruber Jul 23 at 4:06
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    @AlexanderGruber In that sense, I think a (permutation-groups) tag is infinitely more valuable then a (permutation-cycles) tag. This tag could cover orbits (cycles), stabilizers, things of that nature, rather than simply counting permutations from an alphabet. – Morgan Rodgers Jul 23 at 5:10
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    i'd certainly agree with you in a perfect world; however, the synonym was created in the first place due to widespread misuse of permutation-groups to tag elementary group theory questions about permutations. I don't think it had been applied in the way you suggest even once, even though that was its intended purpose. – Alexander Gruber Jul 23 at 6:39
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    What we've been using instead for those types of questions has been group-actions. – Alexander Gruber Jul 23 at 6:42
  • My main reason for creating the tag is precisely the reason Alexander Gruber gave: to make a distinction between abstract algebra permutations and combinatoric permutations. I could not add the (permutation-groups) tag to the questions that I was looking at (I'm not sure how synonyms work on this site), so I created the tag (permutation-cycles) to make this distinction. I felt the name of the tag also made it easier to make the distinction for questions that are elementary and posed by newer users -- the questions I've added the tag to do not use permutations in the context of group actions... – Bill Wallis Jul 23 at 13:18
  • ...and some of them do not explicitly use the group structure of permutations either. My intended usage of the (permutation-cycles) tag would be for questions concerning the permutations themselves in isolation. For example, the multiple representation of permutations, clarifying multiplication of permutations (particularly since this is not covered well in many elementary textbooks)... – Bill Wallis Jul 23 at 13:18
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    ...clarifying classic permutation proofs such as unique parity, and so on. I feel that the distinction is worth being made, but I welcome all criticisms (I'm still learning what makes a good tag). – Bill Wallis Jul 23 at 13:18

Suggestion: eliminate the tag .

The tag was recently introduced. It currently applies to two questions, both of which were asked by who I presume is the tag creator. It seems way too niche to merit a tag, and I suggest that this tag be eliminate.

Reopen the homeomorphism tag

I think that we should have a homeomorphism tag. On the other hand, I am aware of the fact that there was such a tag in the past (before I arrived here) and that, since it was removed, my proposal will almost surely be rejected. But I would like to have an explanation for that. It doesn't seem to be essentially different from the tag, the tag, or the tag, all of which exist. It it certainly seems useful for questions about proving that two topological spaces are (or are not) homeomorphic.

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