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Martin Sleziak
Martin Sleziak
10:17
Kleinian group
In mathematics, a Kleinian group is a discrete subgroup of the group of orientation-preserving isometries of hyperbolic 3-space H3. The latter, identifiable with PSL(2, C), is the quotient group of the 2 by 2 complex matrices of determinant 1 by their center, which consists of the identity matrix and its product by −1. PSL(2, C) has a natural representation as orientation-preserving conformal transformations of the Riemann sphere, and as orientation-preserving conformal transformations of the open unit ball B3 in R3. The group of Möbius transformations is also related as the non-orientation...
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Q: Question/suggestion about a tag (Kleinian groups)

Jan Olav RI am a bit unsure if this should be posted here or in Mathematics, but I try it here. I was surprised to see that there was no "Kleinian groups"-tag at Mathematics and Mathoverflow. I would like to know why. Is it because it has been considered but turned down, or has it never been considered? If...

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Martin Sleziak
Martin Sleziak
12:02
A quick search suggests that there are 64 questions about Kleinian groups on math.stackexchange and 135 on mathoverflow. These all seem to be tagged with some combination of hyperbolic-geometry and geometric-topology though other tags appear as well. On a site with actually hundreds of thousands of questions, are these numbers enough to warrant a special tag? — postmortes 2 hours ago
@postmortes That is a fair point. But there are existing tags with less hit on searches, like ackermann numbers (on overflow) and acyklic orientations. Do you disagree with me that it is a well-established mathematical subject? — Jan Olav R 27 mins ago
it is after all in MSC. (sorry for double commenting, I was too slow with the editing.) — Jan Olav R 20 mins ago
I guess it is self-evident - but I will still point out that this is not a right place to discuss tags on MathOverflow; they have their own meta. (So we should stick with Mathematics.) @postmortes How exactly did you get 64 questions. I only get 33 results. Perhaps you searched for both questions and answers? — Martin Sleziak 43 secs ago
I did not find older messages discussing a tag for Kleinian groups in this chatroom.
SEDE does not return any deleted question with a tag containing the string Kleinian: data.stackexchange.com/math/query/883845/…
And I did not get questions which had such tag at some point in the past, either: data.stackexchange.com/math/query/1105163/…
@MartinSleziak ah, yes, you're right, I wasn't careful enough! Sorry -- and thank-you for double-checking :) — postmortes 1 min ago
One should keep in mind that there are only five slots for tags. If we created too many tags for very specialized topics, there will be questions where more than 5 of the existing tags are suitable. I will add that I did not find older occurrences of a tag for Kleinian groups - I posted the SEDE queries in the tagging chatroom — Martin Sleziak 26 secs ago
@JanOlavR I'm not agreeing or disagreeing with you. Comments are for improving questions and it seems like your question would be better answerable by the community if you provided a modicum of concrete data, like the number of questions you're proposing to tag and explaining why the existing tags/search options aren't good enough. You are free to ignore everything I write. — postmortes 32 secs ago
Since MSC was mentioned, Kleinian groups are 30F40.

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