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    Anton recently merged [point-set-topology] into [gn.general-topology]. I think this was a bad idea! First, the arxiv classification of General Topology "Continuum theory, point-set topology, spaces with algebraic structure, foundations, dimension theory, local and global properties" clearly covers a superset of "point set topology".

    More generally, I get the impression that the "General Topology" arxiv category is widely preceived as "less serious", and perhaps even as an acceptable sacrifice to the amateurs and crackpots (although to a much smaller extend than General Mathematics and History & Overview).


    @Scott: we can recreate the [point-set-topology] tag. Like I said earlier, there were very few posts that used it, so I don't think the merge did much harm. But could you explain what sorts of things would be tagged [point-set-topology]? I think of it as being "anything that's general topology, but isn't anything else specifically." If there isn't a better description, then I think it's fine to not have a separate tag for it.

    Hmm. Arxiv classification notwithstanding, I still don't see any symmetric difference between point-set topology and general topology. E.g., I think we touched on dimension theory in a course I took as an undergrad called "point-set topology".

    About the General Topology section on the arxiv being open to amateurs and crackpots....that I really haven't seen. Would you be willing to give a few examples?

    I just can't imagine a post on MO where some nuance of information would be conveyed between these two tags. Again, I would be grateful if you could provide an example.

    I retract my vilification of General Topology. I was mistaken.

    Do we need separate tags for teaching and mathematics-education?
    • CommentAuthorAnweshi
    • CommentTimeJan 24th 2010

    If mathematics education just means teaching, then it is a misleading euphemism with the connotation that they also care about students' problems.

    • CommentAuthorAnweshi
    • CommentTimeJan 24th 2010 edited


    To remove ambiguity, I agree with Pete that there seems to be no difference between teaching and math education, in the usual meaning they are used.

    Speaking of English, no need to keep reminding me that the language is not my native one. On the other hand if there are spelling mistakes, unnatural expressions, split infinitives etc., then you can point out and I will be most grateful for your help in making me improve.

    • CommentAuthorAnweshi
    • CommentTimeJan 24th 2010

    @Harry. Noted. Thanks. I will introspect more in future about my syntax and meaning.


    "mathematics-education" and "teaching" could be distinct (though they could also be used synonymously). To illustrate, the question applications of Euler-Cauchy ODEs is "mathematics-education" but teaching and students is "teaching". I would definitely like to keep the former on MO and am happy to tolerate the latter so long as there aren't too many of them.

    In case anyone's not clear what I mean, I expect "teaching" questions to get answers of the form "I'm not an expert in education theory, but here's my experience" but "mathematics-education" questions to get answers of the form "Here's an explanation for this mathematical problem at the right level to explain to a load of undergraduates."

    The tags "convex-polytope", "polyhedra" and "polytopes" should be combined.

    There is a technical distinction between a polyhedron and a polytope, namely that polytopes are bounded but polyhedra need not be. No one is observing this distinction and I can't imagine someone who would want to read questions about one and not the other.

    I thought that "polyhedra" live in R^3 and "polytopes" live in R^n.

    Even if this is true, it does not invalidate your conclusion in my mind: the tags are similar enough to be merged.

    Gunter Ziegler's book Lectures on Polytopes supports my definitions.

    OK, no worries. (I can't bring myself to write that wikipedia sup...nope, I really can't do it.) I don't work in the field, so the places where I have seen the terminology used as I suggested above are probably not up to date.

    Presumably we should merge all of them into [polytopes]?


    I prefer convex-polytopes, since it will match more partial strings.


    Merged [polyhedra],[polytopes] ---> [convex-polytopes] and [history] ---> [ho.history-overview].

    btw, @David, you can do this too, now (10k). Click "mod", then "links", then "merge tags".


    Just a thought. Lets say I have [polyhedra] as an interesting tag, will [convex-polytopes] be one to automatically? Now if the answer to the first question is yes I have another thought. Lets say that for some reason I have [polyhedra] as an interesting tag, and [polytopes] as an ignored tag. What will happen to [convex-polytopes]?


    @Scott: 10k users only have access to the "tools" menu, not the "mod" menu. For others who are curious, here's a list of the things 10k+ users have access to.

    • CommentAuthorYemon Choi
    • CommentTimeJan 31st 2010

    Having looked over some of the fa.functional-analysis items, I feel (though not with absolute unswerving conviction) that some of them deserve a sub-heading tag of "banach-spaces" -- within functional analysis, there is I think some divide in emphasis/tone if not in the core fundamentals, between those who look at (say) eigenvalues of unbounded differential operators, and the study of structural properties of Banach spaces.

    But before I start tagging things, I wondered if anyone had any thoughts on whether this seems a good idea. (I know the arXiv doesn't have a separate tag for Banach spaces, but fa.func-an is a very broad label to stick on things.) It seems that since we have at least one expert/doyen of Banach space theory on MO, a finer classification would help to pick out such items for special consideration.

    @YC: Who is the Banach space doyen? Do you mean yourself? I mean no offense; I simply don't know enough to be sure of this. (Except: isn't Tim Gowers also a Banach space doyen?)
    Bill Johnson?
    • CommentAuthorYemon Choi
    • CommentTimeJan 31st 2010

    @Jonas, @Pete: yes, I was thinking of Bill Johnson (I hope he doesn't mind me referring to him as such; it was of course partly tongue-in-cheek). I was particularly amused to see one recent question where I thought "oh, I wonder if the Johnson-Lindenstrauss lemma would be relevant", and to then see the man himself turn up in comments to politely mention it.

    • CommentAuthorJonas Meyer
    • CommentTimeFeb 10th 2010 edited
    I think I read once that tags without homes are automatically deleted after a short amount of time, like a day or so.

    Edit: This was in reply to a since deleted post. If a moderator would like to remove this one, feel free.
    • CommentAuthorLK
    • CommentTimeFeb 10th 2010
    But the homeless point-set-topology tag is alive, and has been for a long time.
    @Harry: I don't understand at all why you think neron-models is not a valid tag. Once again, I worry that you are acting on things which are outside of your actual experience. I for instance have used Neron models in my work, and I certainly don't view them as a special case of motives. The authoritative book on the subject ("Neron Models") does not take this perspective either.

    Have you done research on Neron models? Do you know, for instance, how the torsion subgroup of an abelian variety over a local field depends on the special fiber of its Neron model? If not, why are you involved in this?

    Are you just overly enthusiastic or do you actually believe that, in a site populated by many leading algebraic and arithmetic geometers, you are in some sense an expert on these subjects?
    • CommentAuthorEmerton
    • CommentTimeFeb 10th 2010

    Unless there is a technical reason to want fewer tags, I don't see why more specialized tags can't be kept available. For example, I think that there is only one post with the tag "Hida theory", but that was a very helpful tag for that post; it told me immediately what the topic of the post would be. Likewise with "Neron models". In some sense these are much more informative than the tag "motives", which often means all things to all people.

    Is there a reason to be concerned about the proliferation of tags (as opposed to duplication)?


    I agree with Emerton's question. If a new tag doesn't introduce confusion, then what's wrong with having rather specialized tags. To me it seems natural to introduce more specialized tags since the number of questions is not going to get any less, and a good way to navigate through older questions is by tags.

    @Emerton: I don't think so, no.

    @Harry: I didn't say you were delusional. But it's not tidying up to remove that tag -- it was an important part of the question.

    My position is this: please don't remove a tag based on subject matter that you do not understand. It's not necessary and it's not helpful.
    • CommentAuthorJonas Meyer
    • CommentTimeFeb 10th 2010 edited
    I see that the tag was just restored. I wanted to mention that another possible advantage of keeping the tag is that a user with low reputation may use it in a future question without having to ask for help.

    I don't see any reason to remove the [neron-models] tag in general, or from the specific question. It's not a synonym for another tag and provides good information about the topic of the question. The question should also have the [ag.algebraic-geometry] tag.

    Proliferation isn't a problem so long as the tags provide useful context (ruling out things like [math] or [newbie]).

    In addition to rolling back the removal of this tag, I have added it to two further questions, confirming that I am not being argumentative but really do think it's a useful tag.

    In fact, in the two instances I added it, there were already the maximal number (5) tags on the question, so I had to remove one in order to add neron-models. In each case I removed the tag abelian-schemes. My feeling was that since there were also algebraic-geometry, arithmetic-geometry, number-theory and abelian-varieties tags, this replacement is more descriptive without any serious danger of dropping the question from anyone's attention. (There is, I hope, no one who is interested in abelian-schemes but not in any of those other things?!?)

    Is there any reason to have a tag "lie", in addition to "lie-algebras" and "lie-groups"?

    • CommentAuthorAnweshi
    • CommentTimeFeb 24th 2010 edited

    @David Speyer. It could be useful to keep it to indicate that the questioner is deliberately lying, or to indicate that s/he does not mind lies as answers, etc.. I mean, not all of us are truth-seekers.

    • CommentAuthorjc
    • CommentTimeMay 20th 2010 edited

    This could be questionable, but I noticed that there is both a [symplectic-topology] tag (used 9x) and a [sg.symplectic-geometry] tag (used 54x). (and 6 questions are tagged with both). I would think that anyone interested in one would be interested in the other (and the current use of the tags seems to my non-expert eye to cover the same ground), but I would be happy to hear an explanation if I'm off-base on this.

    edit: for convenience

    [symplectic-topology], 9 questions

    [sg.symplectic-geometry], 54 questions

    Their intersection, 6 questions

    [symplectic-topology] without [sg.symplectic-geometry] 3 questions

    • CommentAuthorPerutz
    • CommentTimeMay 21st 2010
    @jc. The usage of these two "symplectic" tags in, for instance, Chris Woodward's recent question reflects standard usage of the terms. (Probably those questions tagged symplectic topology ought also to be tagged symplectic geometry, but not conversely.)

    Symplectic geometry traditionally includes or overlaps with Hamiltonian dynamics, integrable systems, differential geometry of moment maps, coadjoint orbits and their relation to representations, Poisson geometry, quantization, etc. Symplectic topology refers specifically to the part of symplectic geometry concerned with global problems and global methods. Does this manifold admit symplectic forms? What are the homotopy groups of the symplectomorphism group of this manifold?

    In the 1980s, Gromov and others discovered that these problems usually have different answers to their "linearized" analogues which are problems in differential topology coupled to bundle theory. This discovery led to the growth of the new discipline of symplectic topology, and the terminology emphasizes the difference with differential topology.
    • CommentAuthorjc
    • CommentTimeMay 21st 2010

    Thanks for the explanation, Perutz.

    • CommentAuthorjonas
    • CommentTimeMay 23rd 2010

    [combinatorics] and [co.combinatorics]? The first tag only has two questions.


    Any chance of ditching the tag 'pdf'? It has three questions, one on PDF, two on probability distribution functions (of which one is closed and the other ought to be). As tags go, it's singularly uninformative.

    I propose adding the CS tags from areas on the arxiv (e.g., cs.CC.complexity-theory) and merging tags into these where appropriate. I know the arxiv isn't popular for Theory people but even so, consider the following subset of areas:

    Computational Complexity
    Computational Engineering, Finance, and Science
    Computational Geometry
    Computer Science and Game Theory
    Computer Vision and Pattern Recognition
    Cryptography and Security
    Data Structures and Algorithms
    Discrete Mathematics
    Formal Languages and Automata Theory
    Information Theory
    Mathematical Software
    Neural and Evolutionary Computing
    Numerical Analysis
    Symbolic Computation

    all of which (by my reckoning) have elements that could be construed as fair game on MO.

    I've merged [commutative-rings]->[ac.commutative-algebra] and [ring-theory]->[ra.rings-and-algebras]. See this thread.

    • CommentAuthorVP
    • CommentTimeJul 19th 2010 edited

    Anton, for the record: I objected to the first merge. Why the hurry? Given that merges are irreversible and there wasn't even good case put forth for performing it, don't you think it would have been more considerate to wait for input from other people a while longer?


    Also for the record: shortly after Anton did the merge, I'd been on the verge of doing it myself before noticing this thread.

    • CommentAuthorVP
    • CommentTimeJul 20th 2010

    Scott, my question above is very short and specific. Would you mind answering it directly?

    To clarify: merging proposal was made in a different thread and the merge carried out less than 24 hours later (Harry hadn't yet stated his case by then; I learned about the merge from Harry's response to my objection; I hadn't even see this thread because it was moved to the top after some moderator tweaking). Having been on the verge of doing something is not a matter of record, by the way.


    @VP: I merged the tags before you had voiced your objection. At the time I merged the tags, I assessed things like this. (1) The thread consisted entirely of agreement on the merge and had been up for a while. In particular, three moderators (including myself) had agreed to it. This suggested that there wouldn't be any objection to the merge. (2) There were only a handful of questions tagged [commutative-rings], and looking over them didn't raise any red flags for merging. The small number of questions under the merged tag means that even if the merge is a mistake, little harm is done.

    That said, I understand your objection and I did consider this a borderline situation. I don't think I would have merged the tags (as soon) if the proposal had been up for less time, demonstrated less unanimous support, or if there had been more questions with the [commutative-rings] tag. I'm perfectly happy to follow the policy that moderators wait 24 hours from the time of a merge proposal before merging tags.


    @VP, I answered in the other thread: lack of attention span on the part of moderators, and unwillingness on my part to make todo lists!

    • CommentAuthorVP
    • CommentTimeJul 20th 2010

    Anton and Scott, thank you for your explanation, I understand that it was an unfortunate oversight (and "support" ≠ "no objections raised").

    My perspective is that between 10 and 20 questions with a given tag is close to an ideal situation (not too many to go through, and presents clear evidence of usefulness). By contrast, ac.commutative-algebra, which is top level arXiv category, has over 350 questions. Emerton presented a convincing example where having even one question with a given tag was appropriate. A tag with comparable coverage to [commutative-rings] is [fusion-categories] (11 questions), and for as long as people find it useful, it shouldn't be merged into its top level tag [qa.quantum-algebra] (88 questions).


    Here is a list of tags associated to one question which seem problematic to me. Some of these are obvious, but others are just suggestions.

    [undecidability-results] - merge with a logic tag of some kind?

    [tensor-powers] - merge with [tensor-products]?

    [tensor-categories] - merge with [monoidal-categories]?

    [theory-of-games] - merge with [game-theory]?




    [spam] - merge with [tag-removed]?


    [homological] - merge with [homological-algebra]? (This question also has the tag [algebra].)

    [gt.general-topology] - merge with [gn.general-topology]?

    [group] - merge with []?

    [geometric] - looks like it was an accident

    [line] - looks like it was an accident


    [open] - merge with [open-problem]?

    [operad] - merge with [operads]?

    [metric-spaces] - merge with [mg.metric-geometry]?

    [orbifold] - merge with [orbifolds]?


    [boolean-rings] - merge with [boolean-algebra]?

    [complex-variables] - merge with [cv.complex-variables]?

    [coarse-moduli-spaces] - merge with [moduli-spaces]? (Or at least tag this question [moduli-spaces].)

    [algebraic-integers] - merge with [algebraic-number-theory]?

    [algebraic-numbers] - merge with [algebraic-number-theory]?

    • CommentAuthorWillieWong
    • CommentTimeJul 25th 2010

    [gt.general-topology] is almost surely a typo. The one post in that tag asks if "every closed subset of a infinite dimensional separable Hilbert space homeomorphic to a closed and bounded subset". Somehow I feel that there can be a better tag for that.

    [tensor-powers] may refer to Terry's tensor power trick for analytical estimates. So I don't think it should be merged with [tensor-products]; though the only post in [tensor-powers] is probably something that does belong in the [tensor-products] category. I think that one just needs to be re-tagged.

    I've also wondered about [theory-of-games], but considering that the only post with that tag is by Joel David Hamkins, and about the children's game War, I am somewhat reluctant to merge that into [game-theory]


    Re: [theory-of-games], I guess Joel meant it as a pun?


    Some tags associated to two questions. Most of these seem okay.

    [topology] - merge with [gn.general-topology]?


    [stable-homotopy-category] - merge with [stable-homotopy]?

    [weights] - ambiguous?

    [algebras] - one of these is a mistake

    [duality] - ambiguous?


    [model] - ambiguous?

    [ov.overview] - merge with [ho.history-overview]?

    [groups] - merge with []?