5:03 PM
specific-question This (recently bumped) question is clearly asking for list of proofs: Surprisingly short or elegant proofs using Lie theory. Should one of the tags proofs or slick-proof be added there (or both)?
Of the seven questions tagged proofs, three are also tagged big-list, so maybe this type of question was one of the cases for which the tag was intended.
5:42 PM
Jan 11 '17 at 11:41, by quid
@MartinSleziak the idea ought to be that it is for questions about proofs specifically. But really I think it's not a meaningful tag. I am actually surprised it's around. I do recall slick-proof, which is not much better, and I think we got rid of missing-lemma at one point.
2 hours later…
7:51 PM
7
Let $\lambda$ be a singular cardinal of countable cofinality. Is there necessarily a sequence $\{A_\alpha\mid\alpha<\lambda^+\}$ of countable subsets of $\lambda$, such that $\alpha<\beta$ if and only if $A_\alpha\setminus A_\beta$ is finite? In other words, we know that for $\omega$, there is ...
PCF theory is the name of a mathematical theory, introduced by Saharon Shelah (1978), that deals with the cofinality of the ultraproducts of ordered sets. It gives strong upper bounds on the cardinalities of power sets of singular cardinals, and has many more applications as well. The abbreviation "PCF" stands for "possible cofinalities".
== Main definitions ==
If A is an infinite set of regular cardinals, D is an ultrafilter on A, then we let
c
f
(
∏
A
/
D
)
{\displaystyle cf(\prod...
On Math.SE Asaf always says that new tags should be discussed on meta first; but I guess MO is slightly different :-)
There is a saying that it's easier to apologize later than get permission first. I disagree with that when it comes to new tags. When I see a new tag which wasn't discussed on meta first, I will almost always delete it. Especially if I wouldn't be 168% sure that I'd agree with having that tag on the site. — Asaf Karagila Oct 2 '14 at 4:36
« first day (1610 days earlier) ← previous day next day → last day (2301 days later) »
Transcript for
Jan17
Jan '1818
Jan19
MO editors' lounge
Talk related to editing, tagging and related matters for the s...