« first day (1610 days earlier)      last day (2290 days later) » 

Martin Sleziak
Martin Sleziak
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.
50
Q: Surprisingly short or elegant proofs using Lie theory

Robin GoodfellowToday, I was listening to someone give an exhausting proof of the fundamental theorem of algebra when I recalled that there was a short proof using Lie theory: A finite extension $K$ of $\mathbb{C}$ forms a finite-dimensional vector space over $\mathbb{C}$, so the group of units $K^\times$ wo...

lie-groups lie-algebras big-list
 
Martin Sleziak
Martin Sleziak
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.
It seems that number of question in this tag did not grow since last January.
 
 
2 hours later…
Martin Sleziak
Martin Sleziak
7:51 PM
A new tag pcf has been created recently by Asaf Karagila.
7
Q: "Towers" on singular cardinals with countable cofinality

Asaf KaragilaLet $\lambda$ 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 ...

set-theory lo.logic infinite-combinatorics pcf
PCF theory
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...
Since it is a big topic in set theory, the tag is most likely to be useful.
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)      last day (2290 days later) »