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This tag is used if a reference is needed in a paper or textbook on a specific result.

7 votes

Infinite families in stable homotopy groups

As you probably know, the existence of Greek letter elements relies on the existence of (generalized) Smith-Toda complexes -- the best introduction to those is probably still Section 1.3 of Ravenel's …
Lennart Meier's user avatar
4 votes

Derivators (in English)

A theory of a very similar flavour can be found in a preprint of Jens Franke.
Lennart Meier's user avatar
36 votes

Most important results in 2022

I'd like to mention the resolution of the redshift conjecture for $E_{\infty}$-rings. The latter are a homotopical refinement of usual commutative rings; at least if we restrict to connective ones, we …
4 votes

A Learning Roadmap request: From high-school to mid-undergraduate studies

I don't know how much sense it makes to study books on the topics of the usual first courses at university since this is stuff one learns anyhow at university. This means not that I recommend to study …
12 votes
Accepted

Rational homotopy invariance of algebraic $K$-theory

The theorem can be found in more general form in Land, Tamme On the K-theory of pullbacks, Lemma 2.4.
Lennart Meier's user avatar
13 votes
1 answer
661 views

When is $A\otimes R$ a free $R$-module?

Let $R$ be a commutative ring. If I am not mistaken, there is the following fact: For a finitely generated abelian group $A$, the $R$-module $A\otimes R$ is free if and only if we can write the to …
Lennart Meier's user avatar
20 votes

Who was Hermann Künneth?

For the sake of the readers who are not fluent in German, I provide a translation of the German Wikipedia page (link to the revision at the time of posting this answer): Hermann Künneth (1892-1975) w …
Lennart Meier's user avatar
4 votes

A reference for $\mathbb{A}^1_R$ being a coarse moduli space of the stack of elliptic curves

The following strategy should work although I do not claim that it is the most elegant. Claim 1: The coarse moduli stack of elliptic curves $\mathcal{M}_{1,R}$ is affine. Proof: It is enough to sho …
Lennart Meier's user avatar
6 votes

Good introductory references on algebraic stacks?

I always found Algebraic Stacks by Tomas Gomez to be a very readable quick introduction. It is virtually without proofs but explains on 34 pages the most relevant definitions and constructions and dis …
Lennart Meier's user avatar
20 votes

Examples of algorithms requiring deep mathematics to prove correctness

How about the following problem: Given an integer $n$, how many ways are there to write it as the sum of $k$ squares? Or, equivalently, in $\mathbb{R}^k$, how many lattice points (in the standard int …
22 votes
3 answers
816 views

Boardman's thesis or mimeographed notes

I would like to know if there is some online source where Boardman's 1964 thesis is available or his Warwick mimeographed notes. This is because by what I've heard Boardman's construction has a more m …
Lennart Meier's user avatar
5 votes

Homotopy group action and equivariant cohomology theories

Much has already been said in the other answers and comments, but let me summarize a few points. One way to obtain from a category a 'homotopy theory' (aka an $\infty$-category) is to specify a notion …
Lennart Meier's user avatar
10 votes
2 answers
2k views

Reference for Weighted Projective Stacks

For a sequence of positive integers $a_0, \ldots, a_n$ and a ring $R$, there is a graded ring $R[x_0,\ldots, x_n]$ where $x_i$ is in degree $a_i$. There is a corresponding $\mathbb{G}_m$-action on $Sp …
Lennart Meier's user avatar
5 votes
Accepted

Reference for universal elliptic curves

For any $n\geq 1$, one can define a functor $\mathcal{M}_1(n)\colon \mathrm{Schemes}/\mathbb{Z}[\frac1n] \to \mathrm{Groupoids}$, sending a scheme to the groupoid of elliptic curves over it with a cho …
Lennart Meier's user avatar
5 votes
0 answers
329 views

CW-structure on flag manifolds

I want to apologize in advance if my question is too elementary as I am not an expert in Lie theory. I have posted it before on stackexchange without receiving an answer. Let $G$ be a compact Lie grou …
Lennart Meier's user avatar

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