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7
votes
Accepted
What's the deal with De Morgan algebras and Kleene algebras?
Per request of the OP, I’m reposting my comments as an answer. This is a series of observations without any references; most of these things are well known/easily shown.
Normal forms. … Using De Morgan’s laws, any term can be converted to a CNF: a $\bigwedge$ of a set of clauses, each of which is a $\bigvee$ of a set of literals (= variables and their negations; we specifically allow …
7
votes
Accepted
Number of semistandard tableaux of all possible shapes fitting within some rectangle
I'm converting my comments to an answer. …
1
vote
Is $\mathcal H/\Gamma$ defined over a number field when $\Gamma$ is not congruent?
To convert my comment to an answer: Let $X=\mathbb H^2$ denote the hyperbolic plane and $\Gamma< \Lambda=PSL(2,\mathbb Z)$ a finite-index subgroup. …
4
votes
Third page differential in the Lyndon–Hochschild–Serre Spectral Sequence
I am converting my comments on this question into an answer because I see that they do answer the question. …
4
votes
Topological rigidity of cartesian product with $\mathbb{R}$
Let me convert my comment to an answer: Your expectation is false at least if the dimension of your manifold is $\ge 5$. …
1
vote
Accepted
Shape of convex invariant sets in symmetric spaces
To convert my comments to an answer. Consider the case of convex-cocompact nonelementary subgroups $\Gamma< PSL(2,\mathbb C)$ whose domain of discontinuity in $S^2$ is nonempty (i.e. …
8
votes
Accepted
Relationship between infinite suspension $\Sigma^{\infty}$ of $E_{\infty}$ grouplike space a...
(I'm converting my comment to an answer:)
No, it gives you the infinite delooping of the free symmetric infinity group on the underlying space. …
6
votes
Accepted
Clarification on proof of the algebraic completeness of nimbers
[Converted from a comment into an answer, and expanded with a copy of the statement from Siegel's book.] …
1
vote
Solving $X$ for prescribed $\operatorname{div}(X)$ of compact support
This has been answered well but as a long comment
I would like to say that there is a field $X$ that is bounded by a constant multiple of $|x|^{-2}$. … It is part of the Poincare Lemma (see Spivak's Calculus on Manifolds and convert from forms to vector notation; there is an exposition of that on my web page bterrell.net) that
$$
f(x) = {\rm div\,}\Big …
3
votes
Completing half of Hilbert's program: Foundations that are conservative over Peano Arithmetic
The foundation in this answer is probably a bit weird to work in, but I think it is interesting meta-mathematically and would at least be interesting to compare other foundations too. … I described it in this comment as a "bit lazy" but figured it would still be worth it to post.
Take the language of first-order set theory and add a constant symbol $\mathcal N$. …
5
votes
Accepted
Is every finite lattice isomorphic to a union-closed family of sets containing $\emptyset$?
I am converting my comment into an answer at the request of the proposer. Given $x\in L$, let $S_x=\{y\in L\, :\, y\not\geq x\}$. …
1
vote
Anti-concentration of polynomials on Haar measure
This is slightly too long for a comment, and so I'm posting it as an answer.
It doesn't seem to me like there is a simple "hack" to translate Carbery-Wright to this setting. … Even more simply in your case, all you need is to convert a non-homogeneous anti-concentration statement into a homogeneous one. …
5
votes
Bijections on the set of integer partitions of $n$
I'm converting my comments to an answer.
Let $\mathrm{Par} = \{\lambda\colon \lambda \vdash n, n \geq 0\}$ denote the set of all integer partitions. …
3
votes
The probability that iid draws from a mean zero random variable sum to zero
I guess I can convert my comment to an answer. …
5
votes
Density of a set of numbers whose prime factors are defined by congruences
Sean Eberhard has already answered your question in the comments, but perhaps it's worth mentioning that one can find quite precise information about the general class of problems you are interested in … This will give that
$$\sum_{n\leqslant x} 1_S(n) \asymp \frac{x}{(\log x)^{1/2}},$$
and indeed one can convert this into an asymptotic formula. …