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    • CommentAuthorVP
    • CommentTimeJul 25th 2010

    Quiaochu, can you, please, tell us what is the purpose of this exercise? Plurals and obvious flukes like "spam" deserve no further comment, but what are you trying to accomplish listing all these tags? Many of them are fairly precise and we've recently reaffirmed, I think, that there is no pressure to remove precise tags in favor of general ones or to accomodate someone's momentous desire to hyper-organize, since it's likely to clash with other people's ideas?


    VP, I would appreciate if you commented on the tags individually. I do not think many of them are precise, even the ones that aren't just plurals and flukes.


    @VP: The purpose of this exercise is to keep the tag system on MO healthy. Questionable tags that have very few questions under them (e.g. [surjective]) should be removed so that they cannot be (ab)used by new users who don't know any better. Competing "top level" tags (e.g. [groups] vs []) make it more difficult for people to find things they care about, so they should be merged. I agree that there's no reason to merge a precise tag into a general one (provided that the precise tag is actually qualifies as a topic), but that point seems orthogonal to almost all of Qiaochu's suggestions.

    • CommentAuthorHarry Gindi
    • CommentTimeJul 26th 2010 edited

    I'm against merging [stable-homotopy-category] with [stable-homotopy]. Qiaochu's proposed change would be something like merging the (hypothetical, but nonetheless useful) tag [category-of-sets] with [set-theory], which is significantly less descriptive (the categorical properties of the category of sets aren't the focus of set theory, while category-theorists would have very little to say about set theory).

    Similarly, in this case, category theorists and abstract homotopy theorists answering questions about the first tag don't necessarily care too much about the stable homotopy theory of spaces that honest topologists care about. (Here, honest topologist means someone who works mainly with actual spaces, not model categories or some other kind of abstract nonsense).


    Okay, if I don't hear otherwise, I will make the following merges:

    [spam] - merge with [tag-removed]?
    [gt.general-topology] - merge with [gn.general-topology]?
    [ov.overview] - merge with [ho.history-overview]?
    [complex-variables] - merge with [cv.complex-variables]?
    [groups] - merge with []?
    [group] - merge with []?
    [open] - merge with [open-problem]?
    [operad] - merge with [operads]?
    [orbifold] - merge with [orbifolds]?

    (most of these are "easy" ones, cleaning up the established arxiv categories, or pluralizing)

    I propose we don't further consider the following suggested merges:

    [tensor-powers] - merge with [tensor-products]?     *** decided against, on the basis of Terry's "tensor power trick"
    [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]?
    [theory-of-games] - merge with [game-theory]?
    [stable-homotopy-category] - merge with [stable-homotopy]?

    And I don't have any strong opinion on these: perhaps someone could easily reduce the list by doing a little bit of retagging:

    [metric-spaces] - merge with [mg.metric-geometry]?
    [undecidability-results] - merge with a logic tag of some kind?
    [tensor-categories] - merge with [monoidal-categories]?
    [homological] - merge with [homological-algebra]? (This question also has the tag [algebra].)
    [geometric] - looks like it was an accident
    [boolean-rings] - merge with [boolean-algebra]?
    [topology] - merge with [gn.general-topology]?
    [weights] - ambiguous?
    [algebras] - one of these is a mistake
    [duality] - ambiguous?
    [model] - ambiguous?
    [line] - looks like it was an accident

    And, btw, Qiaochu, thanks for looking through the tags list for these: I think this is constructive and useful. I hope others will chime in with particular opinions, especially about my third group above.


    The tags [realizability] and [borel-sets] are both specific and sporadically useful. However, [borel-sets] could be merged with [descriptive-set-theory], though Borel sets are only a small part of descriptive set theory.


    @Harry: That's a fair argument. I only suggested this merge because the questions in question are not themselves tagged [stable-homotopy], and I wasn't sure if that was intentional.

    @Scott: Thanks. As far as the third group:

    • [tensor-categories] and [monoidal-categories] mean the same thing (right?), but the latter is a healthy tag and the former is only associated to one question.
    • The question tagged [homological] is also tagged [algebra]; probably a typo.
    • One of the questions tagged [algebras] is also tagged [tensor]; again, probably a typo.
    • The question tagged [line] is also tagged [line-bundles]; probably the OP forgot to remove the first tag when he found the second.
    • The question tagged [geometric] is also tagged [geometric-langlands]; probably the same.

    I don't have strong opinions about the others either.


    Okay, I will merge [geometric] and [line] into [tag-removed]. [homological] apparently no longer exists. I'll merge [tensor-categories] into [monoidal-categories] (although my personal preference is for the first term over the second). I'm not going to do anything about the [algebras] tag, but I'd encourage someone else to edit and come up with better tags if they feel like it.


    Okay, I've done these, as well as everything from my first list above.

    Also -- an apparent bug report in the tag merge system. I attempted to merge [group] and [groups] into [] in one go, by putting "" in the "master tag" field, and "group groups" in the "rename /remove tag" field. This had the strange effect of merging everything from [] the wrong way into [groupgroups]. I fixed the problem by hand, but it's worth being aware of.

    • CommentAuthorGjergji
    • CommentTimeJul 27th 2010
    The tags [sum-of-squares] and [sums-of-squares] should probably be merged too. :P

    I just created the tag [model-categories]. Could we merge [model-category] into [model-categories]? We had a discussion about this a week ago on meta, and it made sense (I cited the fact that [schemes], [stacks], etc. are all pluralized).

    Re: Steve Huntsman and adding cs.* tags, I've been occasionally changing complexity-theory tags to, but realized that the question gets bumped to the top when I do so. There are currently 82 questions tagged complexity-theory and 9 with the tag. Could these be merged ?
    I second Suresh's request

    It seems I'm too late to the party here, but there is definitely not a consensus that tensor categories and monoidal categories are the same thing. Here is a counterexample: Definition 1.12.3 in the lecture notes on tensor categories by Etingof, Gelaki, Nikshych, and Ostrik asserts the convention that a tensor category is a locally finite k-linear rigid monoidal category for which End(1) is isomorphic to a fixed ground field k. Unsurprisingly, there are monoidal categories that do not satisfy all of the additional criteria.

    In general, the definition of tensor category seems to vary wildly depending on the author, and possibly even the author's intentions in a given paper. However, as far as I can tell, tensor categories are always additive in the literature, and this is not assumed for monoidal categories. Anyway, if the tag appears again, I would vote against a second merge.


    @Scott: Thanks for the clarification. Sorry about that.

    • CommentAuthorjbl
    • CommentTimeJul 30th 2010
    The tag [meta] serves no identifiable purpose except to label questions destined to be closed.

    I just tried to retag a post as (it's an arxiv category). The name appears to be too long for the tagging system (I used for now). Are there any suggestions on what might be the correct course of action ?


    How about Does that fit?


    I guess that could work.

    • CommentAuthorHarry Gindi
    • CommentTimeAug 8th 2010 edited

    or even, to make it fair? Equal opportunity truncation and all that.


    actually I like that one even better. so it is then


    If nobody objects, I'll merge the following tags into [tag-removed] ... a couple of them look like mistakes anyway:
    [vector], [analytic], [number], [meta], and [thanks]

    Should [complexity-classes] be merged into []?

    @Anton: yes.
    • CommentAuthorWillieWong
    • CommentTimeAug 27th 2010

    Okay, this one is so obvious that I don't think I need to go through the usual procedure of proposing it in a separate thread first:

    Can a moderator merge [dynamical-systems] into [ds.dynamical-systems]?

    • CommentAuthorGjergji
    • CommentTimeAug 31st 2010
    Can someone please merge [sequences] and [sequences and series] as well?

    @WillieWong, done.

    @Gjergji, it's not obvious to me that these should be merged. [sequences-and-series] seems to be used more specifically than [sequences].

    • CommentAuthorWill Jagy
    • CommentTimeAug 31st 2010
    Thierry Zell pointed out that there is no "fair division" or "social choice" or, I suppose, "voting theory" tag,
    There would appear to be a number of possible names for a relevant tag, see

    I was going to explain to him that he had enough points to create a tag himself, but why not ask here for the best choice as there are a few possibilities, then I thought it would be quicker to do it myself.
    [dynamical-systems] should be [ds.dynamical-systems]
    It seems the tag [ho.history-overview] was merged into [ov.overview]. Was this intentional? I think it should have gone the other way around.

    Argh, methinks a moderator has fallen to the completely confusing interface used for tag merging...

    • CommentAuthorVP
    • CommentTimeSep 6th 2010

    I've restarted ho.history-overview tag: it is explicitly mentioned as one of the arXiv subject codes that should be included in every question.


    Meanwhile, the dimension-theory tag seems to have been misused. Up until recently, it was used for dimension theory in the context of commutative algebra/algebraic geometry, but it's now got a few questions in it about Hausdorff dimension/Lebesgue dimension. Should we retag the Hausdorff/Lebesgue dimension questions to something different?


    @Harry: I don't know. But if you google the term "dimension theory", most of the results on the first page is on the other usage. If you search on MathSciNet, dimension theory brings up a lot more than just commutative algebra and algebraic geometry. So I think it'd be unfair to claim the tag for just those fields.

    Now, I don't know the precise meaning of dimension theory in all of those fields, so depending on how the concepts are intuitively related, we could either

    (a) Split the tag up like what was recently done for 'distributions' (in this case the uses in differential geometry, probability, and classical analysis are very different) (this also requires renaming what is now dimension theory: if you just leave the name there unchanged it will still be "misused") or

    (b) Just make sure that the ones dealing with commutative algebra and algebraic geometry gets a proper additional tag, and the others get tagged with general topology or something like that. (Which will make sense if the concepts are not too different.)


    As an aside, the tag "gt.general-topology" should be merged into "gn.general-topology". The arXiv math classification GT is for "gt.geometric-topology".

    • CommentAuthorVP
    • CommentTimeSep 8th 2010

    I've noticed that "ds.dynamical-systems" (arXiv classification) currently only has one article, whereas "dynamical-systems" has over a hundred, and it needs to be merged into the arXiv tag.


    Okay, I thought I'd already done these, but apparently I must have done them backwards. Could someone verify for me that these have worked:

    [dynamical-systems] --> [ds.dynamical-systems]
    [ov.overview] --> [ho.history-overview]
    [gt.general-topology] --> [gn.general-topology]

    @Scott: verified.

    • CommentAuthorVP
    • CommentTimeSep 12th 2010

    Currently, there are 115 questions tagged "matrix" and 15 questions tagged "matrices", with the overlap of 2 questions. I couldn't discern a rational criterion for choosing one over the other. Should these be merged?


    Could we merge [abstract-algebra] into [algebra]?

    • CommentAuthorlouigi
    • CommentTimeSep 29th 2010
    [random-processes] and [stochastic-processes] are two names for the same thing, could those two tags be merged? Thanks.
    On a related note, I recommend changing [markov-chains] to [markov-processes]; the latter is not present but is both appropriate and more general.
    • CommentAuthorWillieWong
    • CommentTimeSep 30th 2010

    [matrix] and [matrices] should be merged (yet again) into one. I think the plural form is the one MO prefers?


    Yes, also [model-category] should be changed to [model-categories].

    • CommentAuthorjbl
    • CommentTimeOct 30th 2010

    Should [lattice] be [lattices]?


    Please merge [ca.classical-analysis] with [ca.classical-analysis-ode].


    There are no existing target tags for the above proposed merges:

    • [lattice] ---> [lattices]
    • [model-category] ---> [model-categories]
    • [abstract-algebra] ---> [algebra]

    so I didn't do these (the merge tool won't let you do a merge if the target tag doesn't already exist). If someone wants to retag one of each of these by hand, I'll do the rest.

    I merged [matrix] ---> [matrices], and [ca.classical-analysis-ode] ---> [ca.classical-analysis] (I wasn't sure which way to merge here, but since the tag without "ODE" was by far more common, I thought this followed the principle of least surprise).

    Could I get a second opinion on [markov-chains] ---> [markov-processes] and [random-processes] ---> [stochastic-processes]? I'm not sufficiently familiar to be sure these are the right merges.


    "Random processes" and "stochastic processes" are indeed exactly synonymous, and the latter is the more common term.

    As Steve Huntsman says, "Markov process" is a more general term than "Markov chain" (although people sometimes refer to any Markov process as a Markov chain). I don't understand why he says [markov-processes] is more appropriate though, since it looks to me like most of the questions tagged [markov-chains] really are about Markov chains. Personally I'd leave that one alone.


    @Scott Morrison: thanks. Sorry for not specifying. I did intent for the merge to be into [ca.classical-analysis], as that is the one suggested in the How to Tag text when you ask a new question.

    @Mark: I think generality is the key factor for appropriateness in a tag that isn't highly populated.