# All Questions

**0**

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**0**answers

5 views

### edge graph reconstruction conjecture : set vs multi set

Why is the edge reconstruction conjecture stated with the deck defined as the multi set of graphs formed by deleting one edge? Can someone give an example of two graphs such that the edge deleted ...

**0**

votes

**0**answers

14 views

### Reformulating Sophie Germain Primes [on hold]

$$\frac{2p+1}{p}=\frac{1}{1}+\frac{1}{p}+\frac{1}{1}$$
Is it enough to first parametrize a proof?

**0**

votes

**0**answers

15 views

### Tarski's undefinability theorem and IF logic

The Tarski undefinability theorem is valid when there are several constrains on the logic on which it is applied. The most important is that the logic mus to be closed under contradictory negation. ...

**1**

vote

**0**answers

14 views

### A topological criterion for connectedness of a semi-ample divisor

I have a half page long proof of the following statement, and I would like to know if this is (a corollary of) a well known statement. Maybe there is a reference or a three lines proof?
Statement. ...

**0**

votes

**0**answers

10 views

### Parametrized cancelations in stable Morse theory

Let $B$ be a closed manifold. Let $\pi : M\to B$ be a submersion such that each fiber is a manifold without boundary. Let $f : M \to \mathbb{R}$ be a function such that the restrictions $f_x$ to each ...

**0**

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**0**answers

15 views

### Are there some algorithms to solve the diagonal matrix $X$ to the following matrix equation?

Suppose $X$ is an unknown $m \times m$ diagonal matrix. Given a scalar $0<c<1$, and a matrix $A$ of $m \times m$ size whose entries $0<A_{i,j}<1$. Are there some algorithms to find the ...

**1**

vote

**1**answer

33 views

### Localization of symmetric monoidal category

Let $\mathcal M$ be a symmetric monoidal category, $S\subset \mathcal M$ a collection of objects and morphisms. I would like to construct the localization $\mathcal M \mathop{\longrightarrow}^T ...

**0**

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**0**answers

28 views

### Does the set of automorphisms of a cyclic group exhibit some sense of randomness?

I prefer to proceed with a concrete example if I may. I appreciate that the answer might well be better explained with group theory, geometry and/or notions from probability theory, which I welcome.
...

**0**

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**0**answers

25 views

### Projection onto $\ell^{2,1}$ ball

Does anyone have an idea how to project onto the $\ell^{2,1}$ ball efficiently, i.e. how to solve
$$ u = \arg \min_u \|u-f \|^2 \text{such that } \left(\sum_i \big(\sum_j |u_{i,j}|\big)^2 ...

**0**

votes

**0**answers

40 views

### Number of Matrices with bounded determinant

Here's my question:
Let $k,B,C$ be positive integers such that $B<C$. Can you give an upper bound for the number of $k\times k$ integer matrices having entries bounded in modulus by $B$ having ...

**0**

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**0**answers

10 views

### Existence and Uniqueness of solution of volterra integral equation of the first kind

$$
\int_0^t k(s,t)f(s)ds=g(t)
$$
To know the existence and uniquness of solution of volterra integral equation(VIE) of the first kind, we differentiate it and convert to the VIE of the second kind.
...

**1**

vote

**0**answers

19 views

### What is the number of noncrossing acyclic digraphs?

A noncrossing graph on $n$ vertices is a graph drawn on $n$ points numbered in counter-clockwise order on a circle such that the edges lie entirely within the circle and do not cross each other.
I am ...

**-4**

votes

**0**answers

32 views

### What are the odds in the card game war that the game will start and finish on the first battle? [on hold]

What are the odds? My 6 year old daughter and I played war. On the first card we both played sevens and the battle bagan. We played three face down and one up and they matched again. Again, we ...

**0**

votes

**0**answers

20 views

### Embedding dimension: local finiteness & intuition for more general spaces

Can every complex analytic space be covered by Stein spaces of finite embedding dimension?
I am almost sure that ought to be true. Here the definition of embedding dimension I have in mind is
$$
...

**0**

votes

**1**answer

89 views

### Examples of nontrivial local systems in Decomposition Theorem

There is a proper map $f: X \rightarrow Y$ of projective varieties. The Decomposition Theorem of Beilinson–Bernstein–Deligne-Gabber states that
$$Rf∗IC_X \cong \oplus_a ...

**2**

votes

**3**answers

266 views

### Reference request: SGA7

I want to read SGA7. Without considering the others SGA and EGA, Which are the textbooks for monodromy theory?

**1**

vote

**1**answer

39 views

### Double quotients of Coxeter groups have the chain property?

Let $(W,S)$ be a Coxeter group with Bruhat order $\leq$ and length function $\ell(w)$.
Definition: a subset $X \subset W$ has the chain property if whenever $x,y \in X$ with $x < y$, there ...

**3**

votes

**2**answers

85 views

### A Lie algebra identity

Let $G$ be a Lie group and $\mathfrak{g}$ its Lie algebra. Fix a basis $e_1,\dots,e_n$ of $\mathfrak{g}$ and let $e^1,\dots,e^n$ be its dual basis. We also use $e^i$ to denote the left-invariant ...

**-5**

votes

**0**answers

29 views

### Precalculus Help? [on hold]

The lengths of the sides in a right triangle form three consecutive terms of a geometric sequence. Find the common ratio of the sequence. (There are two distinct answers. Enter your answers as a ...

**2**

votes

**0**answers

50 views

### Update on list of open problems for Cherednik/Symplectic Reflection Algebras

Background:
There are two lists of open problems about Cherednik or Symplectic Reflection Algebras from 2007: Ian Gordon's Problems, Chapter 9 in Symplectic Reflection Algebras, and Ginzburg & ...

**2**

votes

**1**answer

63 views

### References for the Keisler Order

Are there any good/modern references on the Keisler order. I have been reading Keisler's original paper, "Ultraproducts which are not Saturated", which introduces the order. However it is somewhat ...

**3**

votes

**1**answer

49 views

### $C^\infty$-vectors in general representations of Lie groups on locally convex spaces

This question is related to
this one. Let $G$ be a real Lie group (I should emphasize I only care about ordinary Lie groups, not Lie groups modeled on locally convex spaces or anything like that). In ...

**6**

votes

**0**answers

63 views

### Newton polygons of modular polynomials

This is pretty much straightforward curiosity. Is there anything known about Newton polygons of classical modular polynomials (polynomial relations between $j(\tau)$ and $j(n\tau)$)? I understand that ...

**-1**

votes

**0**answers

39 views

### Question about lim and sup of a function [on hold]

Let f(t,d) be a continuous function in t. Prove that:
$\lim\limits_{m\to \infty}\sup\limits_{t\in[t_1,t_2]}f(t,d_m)=\sup\limits_{t\in[t_1,t_2]}\lim\limits_{m\to \infty}f(t,d_m)$
Does anyone have any ...

**0**

votes

**1**answer

55 views

### Topology on the dual of a Frechet space

If $F$ is a Frechet space, is there any locally convex space topology on the dual
$F'$, such that for each local diffeomorphism $f$ from an open subset $U$ of $F$ to $F$,
the map $U \times F' ...

**2**

votes

**1**answer

87 views

### Interpretation of Hochschild Homology groups

In all the literature I've come across there are many concrete interpretations of the first few Hochschild Cohomology groups. For example $HH^1(A,M)\cong Derivation/Inner Derivations$ etc....
In ...

**4**

votes

**0**answers

37 views

### Multiplicative domains and conditional expectations

Let $M$ be an injective von Neumann subalgebra of $B(H)$. For a completely positive map $\phi:B(H)\to B(H)$, let $Mult(\phi)$ denote be the multiplicative domain of $\phi$. For any conditional ...

**0**

votes

**1**answer

62 views

### Maximize combinatorial sum for boolean function

I am trying to maximize the function
$$ S(f)=\sum_{j=0}^{n-\frac{n-1}{t}}(-1)^j{n-\frac{n-1}{t}\choose{j}}\sum_{i=0}^{\frac{n-1}{t}}(-1)^{f(i-j)}(t-1)^i{\frac{n-1}{t}\choose{i}} $$
for a function ...

**-6**

votes

**0**answers

38 views

### solve for three unknowns. [on hold]

Apple cost 97 dollars. Orange cost 56 and lemon cost 3. The total amount spent is 16047 dollars and total fruits bought is 240 and each one is bought atleast one. Calculate how many of each have been ...

**0**

votes

**0**answers

59 views

### Rationally building bridges from Jacquet-Langlands to Langlands functoriality conjectures

For now I mainly worked on very classical proofs (viz. Bolte & Johansson, Bergeron) of the Jacquet-Langlands correspondence, but I hope to be able to understand in what this special case lead ...

**4**

votes

**0**answers

62 views

### The (global) theory of Borel equivalence relations

What do we know about the complexity of the theory of Borel equivalence relations, with the Borel reducibility order $\leq_B$?
That is, let $\mathcal{B}$ be the set of all Borel equivalence ...

**3**

votes

**0**answers

79 views

### If $G$ is compact, $H \leq G$ open, $V$ an irreducible $H$-rep, is $\text{Ind}_H^G$ semisimple?

Let $G$ be a compact group, $H$ a normal open subgroup, and $K$ a $p$-adic field (so that not all $G$-reps with coefficients in $K$ are semisimple). Let $V$ be a topological $K$-vector space with ...

**2**

votes

**1**answer

67 views

### Graphs where each edge belongs to the same number of 1-factors

Let $G$ be a simple connected graph that has at least one 1-factor. We'll define:
$G$ has property A iff it is edge-transitive.
$G$ has property B iff each edge belongs to the same number of ...

**1**

vote

**2**answers

72 views

### Estimate maximal coefficient of a polynomial from a circle containing all roots

Suppose I have a polynomial
$$
p(x)=\sum_{i=0}^n p_ix^i.
$$
For simplicity furthermore assume $p_n=1$.
As it is well known we may use Gershgorin circles to give an upper bound for the absolute ...

**0**

votes

**0**answers

30 views

### On existence of right units with control of their norms [on hold]

Does, there exist a Banach algebra with a family of right units with norms converging to 1, but without right unit of norm 1?

**-2**

votes

**2**answers

83 views

### Lack of parabolicity of PDE due to invariancy under diffeomorphisms?

Let a nonlinear differential equation is invariant under all diffeomorphisms, then we get lack of parabolicity?

**3**

votes

**1**answer

126 views

### Ergodic theory reference for converging sequences of matrices

I have been told that the following is a well known theorem in ergodic theory & have been given the book by Furstenberg as a reference. However, I cannot find such a statement in it. Would anyone ...

**5**

votes

**1**answer

175 views

### Is the Tate conjecture known for etale covers of products of curves

Let $X$ be a (smooth projective geometrically connected) surface over a finitely generated field $k$. The Tate conjecture predicts that, for $l$ a prime number invertible in $k$, the Chern class map ...

**-1**

votes

**0**answers

46 views

### Property of $\limsup$ in $\ell_1$ [on hold]

Let $w$ be any element in $\ell_1$, and $(w_n)$ be a bounded sequence in $\ell_1$ that converge to 0 pointwise. I want to prove
...

**3**

votes

**1**answer

203 views

### Lower bound for a prime gap occurring infinitely often

In his striking paper of may 2013, Zhang showed the existence of an even integer $g\lt 70,000,000$ such that $g$ is a prime gap occurring infinitely often. What is the best unconditional lower bound ...

**5**

votes

**1**answer

45 views

### In the definition of the Heegard Floer surgery exact triangle, what exactly is the correspondence between Whitney triangles and periodic domains?

I'm reading Osváth-Szabó's notes on Heegard Floer homology, in particular about the surgery exact triangle.
On page 14 (numbered 42 on the document), they describe an isomorphism between the space of ...

**7**

votes

**1**answer

424 views

### Tight prime bounds

This is a cross-post of this question on MSE. I would not usually do this, but have decided to in this case since it has had no responses having been posted as a bounty question. I did not delete the ...

**1**

vote

**0**answers

40 views

### Tensor product of commutators vs. commutator in a tensor product

Let $R$ be a (noetherian) commutative ring, and let $V$ and $W$ be finitely generated free $R$-modules. Let $X \subseteq \mathrm{End}_R(V)$ and $Y \subseteq \mathrm{End}_R(W)$ be finite subsets, and ...

**1**

vote

**1**answer

145 views

### Integer points on $y^2=x^2-x^3+x^4$

Does the Diophantine equation $y^2=x^2-x^3+x^4$ have solutions other than
$x=1,y=1$? Interestingly, the Diophantine equation $y^2=x^2-x^3+x^5$ has such solutions: $x=3,y=15$, $x=5,y=55$, ...

**10**

votes

**2**answers

379 views

### History of the connection between Riemann surfaces and complex algebraic curves

As noted in the question "Links between Riemann surfaces and algebraic geometry", there are strong connections between Riemann surfaces and algebraic geometry - for example, compact Riemann surfaces ...

**2**

votes

**0**answers

27 views

### Cusp points in Alexandrov spaces

Given a space of bounded integral curvature (by which I mean a topological surface with an intrinsic metric, such that the sum of excesses of any finite collection of non-overlapping simple triangles ...

**-1**

votes

**0**answers

70 views

### Long cycles in $\text{Sym}(n)$ [on hold]

Let $x,y \in \text{Sym}(n)$ (symmetric group on $\{ 1,2,\ldots,n \}$) and $z:=xy$.
Question: What non-trivial sufficient conditions (on $x$ and $y$) for $z$ to be a cycle of length $n$ do we know?
...

**2**

votes

**0**answers

29 views

### Looking for N-dimensional spheres in the configuration space of the colorful Tverberg problem

Here we use standard notation for Tverberg's theorem: Dimension $d$, number of partition blocks $r$, and $N=(r-1)(d+1)$.
The configuration space of Tverberg's theorem is the simplicial complex ...

**2**

votes

**1**answer

39 views

### Are lightface \Delta-1-1 classes of reals describable with hyperarthmetic formulae?

I'd appreciate if someone could check my reasoning. Suppose $S$ is a lightface $\Delta^1_1$ class of reals. I want to argue that there is a computable $\Delta^0_\alpha$ formula $\phi(Y)$, for ...

**-1**

votes

**0**answers

49 views

### Basis for the rational functions [on hold]

The rational functions $f(x)$ are given by $f(x) = \frac{P(x)}{Q(x)}$ where $P(x)$ and $Q(x)$ are polynomials. What bases for the rational functions are generally used in numerical analysis?