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There used to be a "permutations-groups" tag, which I don't see anymore. What happened to it? Can it be put back?

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  • $\begingroup$ Tags are managed on a Community basis, and you'll find a number of related posts here at Meta.Math.SE (to where your Question was migrated). $\endgroup$ – hardmath May 14 '16 at 14:34
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It is quite easy to see that the tag is now a synonym of permutations.

You could check this simply in the list of tags. (When you start to type permu... you are offered the tags with names containing this string. Then you can click on the tag to find more information.) Or you could check the list of tag synonyms. (Where you can see that the synonym was suggested on March 6 2013 and it was approved relatively recently, on April 20 2016.1)


Maybe it is worth mentioning that tag synonyms are often discussed on meta before they are created. Typically in threads like http://meta.math.stackexchange.com/questions/22348/tag-management-2016 (or older editions of this thread), but if there is a more extensive discussion, there might be a separate question. I do not recall whether this particular tag synonym was discussed on meta, but if it was I was not able to find a post where it was discussed.

Some basic information about tag synonyms can be found here: What are tag synonyms and merged tags? How do they work?


Let me also address the last part of your question: "Can it be put back?"

Only the moderators can undo the tag synonyms. But they will not do so without a good reason. So probably the way to go would be to post a question here on meta and put forward some arguments why you think the two tags should be separate. You can find a bit about this in the section entitled "How can I delete/reverse/undo bad tag synonyms?" in What are tag synonyms and merged tags? How do they work?

I should probably also point out that even if the tag synonym is cancelled, that does not mean that questions which were synonymized as to will get the original tag after the synonym is cancelled. And important think here is whether the tags were only synonymized, or they were also merged. See here for more details: What happens with the tagged questions when a tag-synonym is cancelled?


1 I have removed this after Daniel Fischer's comment. It seems that the meaning of the dates shown in that list is not entirely clear to me.

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  • $\begingroup$ Yes, I saw that. But this doesn't explain why the permutations-groups tag disappeared. It's not quite a synonym for permutations. If you can add it back, I would appreciate it. I don't have enough rep to do it myself. $\endgroup$ – svsring May 14 '16 at 15:52
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    $\begingroup$ @svsring BTW you're spelling the tag name wrong. It is permutation-groups, not permutations-groups. It did not disappear, it is now a synonym of another tag, as you can find out by checking this link. I tried to answer your question which was: "What happen to this tag?" If you were already aware that it is a synonym and your intention was to oppose the synonymization of those two tags, you should have worded your question differently. $\endgroup$ – Martin Sleziak May 14 '16 at 15:56
  • $\begingroup$ The synonym was created on the sixth of March 2013. Perhaps there was some discussion then. Don't know how you searched, if you searched under the assumption that the synonym is new, you may have looked in the wrong places. $\endgroup$ – Daniel Fischer May 14 '16 at 16:09
  • $\begingroup$ @DanielFischer If needed, we can continue this discussion in chat. (It is a kind of meta-discussion, since we want to know whether there was a previous discussion about the issue.) $\endgroup$ – Martin Sleziak May 14 '16 at 16:21
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    $\begingroup$ You're misreading the synonyms page (it's easy to do that). The "Last" column lists when the synonym was last applied, not when it was approved. It was when this question was asked. $\endgroup$ – Daniel Fischer May 14 '16 at 18:12
  • $\begingroup$ Hmm, although, permutation-groups seems to still have existed in July 13. So at least the tags weren't merged then. $\endgroup$ – Daniel Fischer May 14 '16 at 18:19
  • $\begingroup$ @DanielFischer Thanks for the clarification regarding the dates in the synonym list. I have edit my post. $\endgroup$ – Martin Sleziak May 14 '16 at 18:42
  • $\begingroup$ @MartinSleziak The reason for putting back the permutation-groups tag is that the theory of permutation groups is an area of its own. Topics like permutation-avoiding patterns are within the topic of permutations and often do not use notions from group theory. Permutation groups is also a subject of growing importance with more applications - for example, it received a lot of attention recently due to the graph isomorphism problem. $\endgroup$ – svsring May 15 '16 at 11:22
  • $\begingroup$ That's not good that even after re-introducing the permutation-groups tag the earlier questions in permutation-groups might not get back their original tags. What if I want to search for questions/answers in permutation groups per se and not just permutations. $\endgroup$ – svsring May 15 '16 at 11:24
  • $\begingroup$ @svsring As I wrote above, if you think that there are legitimate reason why the tag synonym should be cancelled, you should post a new question on meta. (I doubt that many people will notice your comment here. And also if there is separate question about this, other people can say what their opinion was.) $\endgroup$ – Martin Sleziak May 15 '16 at 11:42
  • $\begingroup$ The other possibility would be to edit this question. (But like this possibility less. In general, changing the question after in a way which invalidates the answer is discouraged.) Or course, it is also possible that I have misunderstood your question and did not answer what you were asking. (But the way you question was phrased, for example saying that you do not see the tag, sounded to me like you were unaware that the two tags are synonyms. Which is why I posted an answer explaining that they are and how the tag synonyms work.) $\endgroup$ – Martin Sleziak May 15 '16 at 11:44

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