# Would tags such as “ultrafilters” or “Stone-Cech compactification” be too specific?

I've noticed that one question was recently tagged . (It is the only question having this tag at the moment.)

I was thinking about a few related tags, which might perhaps be useful; but I wanted to ask about the opinion of other users before creating any of these tags. (I might be biased, since I am interested in these topics. And of course we have 5 tags limit, so we should not overtag.) And it was also advised here: If you are not sure whether a tag belongs, bring it to Meta.

Do you think that tags like , , or would be too specific?

Some arguments why I think these tags would be reasonable:

Aside note: Do you think it would be reasonable to make one big thread for questions related to proposed or newly-created tags, in the same way as we did for Tag merging and synonyms ?

EDIT: I believe 6 upvotes for Asaf's post can be understood as support for his suggestion, which was tag and one common tag for filters and ultrafilters. He has already started . I've edited tag-wiki for filter. Now Asaf also created tag and added tag-wiki. I'll try to add a few questions in the next days, so that the tag is not automatically deleted for having no questions. (This will also have the effect that a few more people will be aware of this tag, since they will see it used on the main page.)

I am not entirely sure about the preference of singular/plural in tag names; however I was not able to create tag, I've got the following warning: Creating the new tag [filters] is not allowed since the tag [filter] already exists. If you think this new tag should be allowed, raise it on meta.

• I think that [filter] should be renamed to [filters]. – Asaf Karagila Jun 10 '12 at 8:19
• I agree - that's why I wanted to remove filter and create filters instead. But the software did not allow me to do this. – Martin Sleziak Jun 10 '12 at 8:25
• Let us try, untag and then re-tag. I untagged, but it may take a few minutes before the system notices that. Edit: I think that the tag wiki may be preventing the dissipation the [filter] tag. – Asaf Karagila Jun 10 '12 at 8:38
• I've put the last version of tag-wiki and excerpt here: pastebin.com/xm8XKUrq So we will not lose it if the tag is deleted. However, I don't think tag-wiki matters; IIRC algebra tag disappeared and it had non-empty tag wiki. – Martin Sleziak Jun 10 '12 at 8:44
• Very good, let us wait a day or so. – Asaf Karagila Jun 10 '12 at 8:47
• @Asaf It seems that empty tags are deleted once a day. See also this answer – Martin Sleziak Jun 10 '12 at 8:47
• Let the games begin! – Asaf Karagila Jun 11 '12 at 5:41
• Just a suggestion for tag editing. I think it's good to include the relevant meta thread in edit summary, so that the people who look at the history of revisions know what's goging on. I was doing so e.g. for algebra retagging, see e.g. here and also for these two new tags, example is here. – Martin Sleziak Jun 12 '12 at 6:37

I remember once walking in the library and seeing huge books on a single molecular structure. I know that there are books over books written on Mozart's symphonies, etc.

The fact that something has a book, a handbook, or even a whole publishing company devoted to it has little to do with the question whether or not this site should have a specific tag.

Remember that this is not quite the research site, so the fact there are books on the topic need not imply that there are enough non-research questions to make the tag useful. For example see which currently host about five questions.

With this breath I should also say that I am in favor of or , this is an exclusive or. Both would be too much in my opinion. Compactification seems reasonable, but Stone-Cech seems over-specific. Instead both, however, I suggest which would also host questions about compactness in general.

• So the compactness tag would include compact spaces, locally compacts spaces, compactifications and other related topics, correct? – Martin Sleziak Jun 8 '12 at 15:39
• @Martin: Yes. More or less. – Asaf Karagila Jun 8 '12 at 15:44
• @Martin: I kicked off the compactness tag, I have to admit that it has been a while that I was thinking that this tag is suitable (I was thinking about a filter related one too, but less often). – Asaf Karagila Jun 8 '12 at 18:58
• Thanks for starting the tag. Do you think it would be useful to include in the tag wiki, that it is intended for related topics (like local compactness, compactification), too? – Martin Sleziak Jun 10 '12 at 8:02
• @Martin: Probably, I wanted to get the tag wiki started too but I didn't know how far to take it. There is so much to say about compactness and its related topics... – Asaf Karagila Jun 10 '12 at 8:18
• I've noticed only now that you've mentioned variants of compactness and compactifications in tag excerpt. I think that is sufficient. (For some reason I only looked at tag-wiki and did not notice that tag-excerpt is different.) – Martin Sleziak Jun 10 '12 at 8:23
• FWIW: I agree with the use of a more general compactness tag as Asaf proposed. – Willie Wong Jun 11 '12 at 7:32

If I'm doubtful about whether a new tag is appropriate, I apply the following tests:

• Can I imagine at least two other users independently deciding that this tag is worth using or searching for? (This is a very weak test but any tag that it rejects should definitely not be used.)
• Will any question that falls under this tag already contain this tag in the text? In other words, is this tag already a viable search term for any questions it might apply to? If so, there's no reason for the additional information in the tag. (I think fails this test.)

I can imagine objections to the second test and probably there are tags that fail it that I would still use for other reasons, but I think it's not a bad guideline.

• If you search "compactness" you have ~450 results; if you search "compact" you get >2000 results. I haven't began looking for variants (compactification; locally compact; etc.) but I believe that your second test supports my idea for a [compactification] tag. – Asaf Karagila Jun 8 '12 at 19:19
• Well, the fact that questions about filters and ultrafilters can be found using the keywords is not the same thing as tags - for example it's not possible to add it between favorite tags. I agree about Stone-Cech compactification being too specific and starting more general tag compactness seems to me a good solution. What do you think about filters tag? – Martin Sleziak Jun 8 '12 at 19:37
• This is no longer relevant - since I agreed that Stone-Cech compactification is too specific topic to deserve its own tag. But out of curiosity I've tried whether I am able to find questions which might get this tag and do not contain the words Stone-Cech compactification (=your second test). Examples: Points in $\beta\omega$, Addition on ultrafilters is non-commutative and Set of ultrafilters $\beta\mathbb N-\mathbb N$ is not separable. – Martin Sleziak Jun 10 '12 at 9:23