@quid: done

@Will: merged

@Willie: merged.

There is a tag "history" with about ten questions. I think this could/should be merged into ho.history-overview.

In addition there is a single one tagged ho.historical-overview that also should be merged (since it is only one I could do so myself but the question is very old, and since I am already mentioning history tags I thought I leave it for the moment)

Thanks in advance!

There are eight questions tagged "group-theory", please, merge into "gr.group-theory". Thanks in advance!

Added: analogous problem for "number-theory" (seven questions)

Added 2: likewise for "numerical-analysis"

AFAIK the default for a tag-name of object-type is plural (according to some long ago agreed upon convention). This is not totally uniformly done though (yet might not be worth fixing).

However, there are some instances where both singular and plural exist, yet the singular is frequent and the plural one very rare (indeed unique!). To have both seems quite unfortunate, yet I am hesitant to simply 'kill' the more correct though infrequent ones.

The examples I am presently aware of are:

hilbert-space(s) 93 vs 1 unitary-representation(s) 27 vs 1 blow-up(s) 37 vs 1

So this is either a request for the merges singular to plural or a request for permission for me 'killing' the plural ones.

Thank you François G. Dorais! Some more findings (where more than I am feeling comfortable to do manually or things I do not want to reactivate are effected):

Several arXiv-like tags, mistyped, or just missing the prefix or otherwise extremely close, and would need merging into the arxiv one:

statistics -> st.statistics

gt.general-topology -> gn.general-topology (yet not gt.geometric topolgy :-) )

ag.algebraic-topology -> at.algebraic-topology

k-theory -> kt.k-theory-homology (this might be debatable, but still seems to make sense, IMO)

functional -> fa.functional-analysis (at the moment there seems to be no single usage of this tag in a truly meaningful way, yet on the other hand it is sometimes abused as building block of "functional analysis"; if ever there is a need the plural "functionals" could be created; yet now it would seem renaming is a lot worse than just merging)

category -> ct.category-theory (at the moment there is just one tagged like so, but I do not want to bump that one)

control-theory -> oc.optimization-control (same as above)

number-theory -> nt.number-theory

numerical-analysis -> na.numerical-analysis (I mention the last two again, as due to my sub-optimal way of reporting them earlier I believe they were overlooked)

Some singular/plural issues (where both exist):

curve -> curves

journal -> journals

manifold -> manifolds

norm -> norms

tensor-product -> tensor-products

Some other things

linear -> linear-algebra (I checked this makes sense at the moment; in some cases manual changes would be "cleaner" as they would not leave tangling 'algebra' tags but 'algebra' seems "lost" as a tag anyway so it might not be worth the bumps)

complexity -> computational-complexity (also makes sense at the moment)

community-wiki -> tag-removed (here I am not sure, but to have three out of many cw-questions tagged cw seems pointless yet could have the bad side-effect that some new users might think tagging like so is what "making community-wiki" means)

Thanks again! Another weekend, another list :)

Singular/plural duplicates (I only give the singular to be merged into the plural):

derived-functor

finite-group

galois-representation

graph-coloring

line-bundle

locale

perfect-matching

quiver

random-graph

semiring

simplicial-complex

Other 'duplicates' or clear 'errors', sometimes I am not sure which form is better

nonstandard-analysis <-> non-standard-analysis

preduals <-> pre-duals

char-p -> characteristic-p ; in addition there is also positive-chracteristic (perhaps in fact both former ones should go into this one)

reference -> reference-request

refer -> reference-request

ha.harmonc-analysis -> harmonic-analysis (no arviv cat.)

geometric-topology -> gt.geometric-topology

Near duplicates (perhaps some are debatable)

dgalgebra -> dg-algebras (at least I believe this makes sense)

derived -> derived-algebraic-geometry (there is only one use of derived)

height-functions -> heights (or the other way round)

algebraic-numbers -> algebraic-number-theory (the former is only used once while the tag is old)

convex -> convexity (the convex tag is somewhat harmful as it "distracts" from convex-something tags; and I think this makes sense for all tagged like so at the moment; there was one where convex-optimization was better I retagged that one manually)

inner-model-theory <-> inner-models (perhaps?)

harmonic -> harmonic-functions (the latter does not exist, but I think it fits for all current uses while I am slightly worried to see 'harmonic numbers' for example making 'harmonic' a strange mix; there is perhaps one exception a question on hermonic polynomials, but since these are AFAIK also harmonic functions it is not so bad)

computability -> computability-theory

real -> real-analysis (seems to make sense at the moment, and real is perhaps a tag to be eliminated)

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Added

A new singular/plural

arithmetic-group -> arithmetic-groups (the correcter plural is new)

And another arXiv without prefix

differential-geometry -> dg.differential-geometry (11 questions)

One more close duplicate

hyperbolic -> hyperbolic-geometry (the tag hyperbolic was somewhat recently born as a broken hyperbolic-geometry; this resurfaced on the front page, which I thus fixed right away, another usage of it was for hyperbolic pde, I created that tag now and retagged one; the remaining is again hyperbolic-geometry)

The merge of inner-model-theory and inner-models that quid just made happen is inappropriate in abstract (I didn't check the questions that had one or the other to see how the tags were originally used). We use inner models in all sorts of settings where none of the definability or canonicity considerations of inner model theory are required or even appropriate.

I retagged the one question to which not even squinting the inner-model-theory tag applies. I think we should keep both tags, even if after my retagging, only one question has the inner-models tag, and very very few have the other. Some of the other questions, I wouldn't have used either tag for them, but inner-model-theory seems more appropriate than the other. (Most likely there are several questions in set-theory that could have been tagged inner-models as well. If I find time, I'll post a list or something.)

Andres, none of the questions tagged inner models (including the one you retagged) had much to do with inner models. I think removing the tag would be more appropriate than adding it back.

This is more a question than a direct suggestion:

There is an (established) tag 'continuum-hypothesis'. Somewhat recently a tag 'gch' got created in addition (it has now 2 questions tagged like so, the second by me, when an old question became reactivated.) Yet, just know a question got asled that seems directly related to the generalized continuum hypothesis but is still tagged only continuum-hypothesis.

In my mind this raises the question whether it is useful to have both tags, for general "size" considerations but even more so since this latest question reinforced my general conviction that consitent usage of fine-grained tags simply is unlikely to happen.

Could the pluralized 'continuum-hypotheses' as common tag makes sense?

@Andres Caicedo: not to be argumentative but since I really do not understand this: if you think (as it seems you do) it is relevant to have these separate tags, why didn't you retag the (IMO) clearly mistagged one to which you contributed (just shortly after being made aware of the issue)?

Some new essential duplicate and 'errors':

mathematical-physics -> mp.mathematical-physics

quantum-group -> quantum-groups

computabilty -> computability-theory

topos->topoi

ha.homological-algebra -> homological-algebra

refe -> reference-request (or tag-removed as the question is already tagged reference request)

graph.theory -> graph-theory

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Some more complicated ones:

derived-categories got created the 'wrong' singular exists with about 100 questions. (This could be a good tactic for getting a taxonimist tag; search a singular tag with a lot of use and create the plural ;D)

Not sure what to do with

examples-counterexamples

AFAIK this is math.SE practise, we have both separately; the current one asks for examples and I am under the impression OP only used it out of math.SE habit. (I once had a conversation on a similar instance where this was given as reason.)

In fact, I just noticed we have

counter-examples and counterexamples (and examples)

as tag.

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One possibly controversial one:

Recently non-associative-algebras and nonassociative-algebra got created (by different users).

The later usage is more like algebra as field and not structure. So, in principle, one could say there is a difference; but due to the general scarcity my personal opinion would be that perhaps one of the two would suffice. Likely i'd preserve the latter.

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Thanks in advance for merges!

complex-variables -> cv.complex-variables

And, at the moment the five question tagged differential could be merged into dg.differential-geometry (I just extracted one where the also existing differentials seemed needed).

Do we really need a [dependent-choice] tag? There are two questions, one which seems to fit (and is tagged) under [axiom-of-choice]; and another which seem to have no business being tagged under [dependent-choice] at all.

Asaf & Quid, go ahead an retag these (not all at once). Thanks!

Any proposals for what to do with the [elementary] tag? Qualifier tags are not a great idea but this one seems to be used quite a lot, not necessarily for bad reasons. Does anyone ever search for this tag?