Let $\alpha :\,G\,\curvearrowright \,M$ be a spatial action of a countable abelian group on a “spatial” von Neumann algebra $M$ and let $S$ be its unital subsemigroup with $G\,=\,{{S}^{-1}}S$. We explicitly compute the essential commutant and the essential fixed-points, modulo the Schatten $p$-class or the compact operators, of the ${{w}^{*}}$-semicrossed product of $M$ by $S$ when ${{M}^{'}}$ contains no non-zero compact operators. We also prove a weaker result when $M$ is a von Neumann algebra on a finite dimensional Hilbert space and $\left( G,\,S \right)\,=\,\left( \mathbb{Z},\,{{\mathbb{Z}}_{+}} \right)$, which extends a famous result due to Davidson (1977) for the classical analytic Toeplitz operators.

Parts of the Brunn–Minkowski theory can be extended to hedgehogs, which are envelopes of families of affine hyperplanes parametrized by their Gauss map. F. Fillastre introduced Fuchsian convex bodies, which are the closed convex sets of Lorentz–Minkowski space that are globally invariant under the action of a Fuchsian group. In this paper, we undertake a study of plane Lorentzian and Fuchsian hedgehogs. In particular, we prove the Fuchsian analogues of classical geometrical inequalities (analogues that are reversed as compared to classical ones).

Suppose that $G$ is a finite group and $H$ is a subgroup of $G$. $H$ is said to be $s$-semipermutable in $G$ if $H{{G}_{p}}\,=\,{{G}_{p}}H$ for any Sylow $p$-subgroup ${{G}_{p}}$ of $G$ with $\left( p,\,\left| H \right| \right)\,=\,1$; $H$ is said to be $s$-quasinormally embedded in $G$ if for each prime $p$ dividing the order of $H$, a Sylow $p$-subgroup of $H$ is also a Sylow $p$-subgroup of some $s$-quasinormal subgroup of $G$. In every non-cyclic Sylow subgroup $P$ of $G$ we fix some subgroup $D$ satisfying $1\,<\,\left| D \right|\,<\,\left| P \right|$ and study the structure of $G$ under the assumption that every subgroup $H$ of $P$ with $\left| H \right|\,=\,\left| D \right|$ is either $s$-semipermutable or $s$-quasinormally embedded in $G$. Some recent results are generalized and unified.

Let $G$ be a graph and let $\tau $ be an assignment of nonnegative integer thresholds to the vertices of $G$. A subset of vertices, $D$, is said to be a $\tau $-dynamicmonopoly if $V\left( G \right)$ can be partitioned into subsets ${{D}_{0}},\,{{D}_{1}},\,\ldots \,,\,{{D}_{k}}$ such that ${{D}_{0}}\,=\,D$ and for any $i\,\in \,\left\{ 0,\,\ldots \,,\,k-1 \right\}$, each vertex $v$ in ${{D}_{i+1}}$ has at least $\tau \left( v \right)$ neighbors in ${{D}_{0}}\cup \cdots \cup {{D}_{i}}$. Denote the size of smallest $\tau $-dynamic monopoly by $\text{dy}{{\text{n}}_{\tau }}\left( G \right)$ and the average of thresholds in $\tau $ by $\bar{\tau }$. We show that the values of $\text{dy}{{\text{n}}_{\tau }}\left( G \right)$ over all assignments $\tau $ with the same average threshold is a continuous set of integers. For any positive number $t$, denote the maximum $\text{dy}{{\text{n}}_{\tau }}\left( G \right)$ taken over all threshold assignments $\tau $ with $\bar{\tau }\,\le \,t$, by $\text{Ldy}{{\text{n}}_{t}}\left( G \right)$. In fact, $\text{Ldy}{{\text{n}}_{t}}\left( G \right)$ shows the worst-case value of a dynamicmonopoly when the average threshold is a given number $t$. We investigate under what conditions on $t$, there exists an upper bound for $\text{Ldy}{{\text{n}}_{t}}\left( G \right)$ of the form $c\left| G \right|$, where $c\,<\,1$. Next, we show that $\text{Ldy}{{\text{n}}_{t}}\left( G \right)$ is $\text{coNP}$-hard for planar graphs but has polynomial-time solution for forests.

The prime vertex graph, $\Delta \left( X \right)$, and the common divisor graph, $\Gamma \left( X \right)$, are two graphs that have been defined on a set of positive integers $X$. Some properties of these graphs have been studied in the cases where either $X$ is the set of character degrees of a group or $X$ is the set of conjugacy class sizes of a group. In this paper, we gather some results on these graphs arising in the context of direct product of two groups.

A surface $\sum$ endowed with a Poisson tensor $\pi$ is known to admit a canonical integration, $G\left( \pi \right)$, which is a 4-dimensional manifold with a (symplectic) Lie groupoid structure. In this short note we show that if $\text{ }\!\!\pi\!\!\text{ }$ is not an area form on the 2-sphere, then $G\left( \pi \right)$ is diffeomorphic to the cotangent bundle $T*\sum$. This extends results by the author and by Bonechi, Ciccoli, Staffolani, and Tarlini.

This paper is concerned with the study of the regularity for the multisublinear maximal operator. It is proved that the multisublinear maximal operator is bounded on first-order Sobolev spaces. Moreover, two key point-wise inequalities for the partial derivatives of the multisublinear maximal functions are established. As an application, the quasi-continuity on the multisublinear maximal function is also obtained.

Every 4-uniform hypergraph on 9 vertices with at most 25 edges has property $\text{B}$. This gives the answer ${{m}_{9}}\left( 4 \right)\,=\,26$ to a question raised by Erdős in 1968.

We study the restriction of Bump–Friedberg integrals to affine lines $\left\{ \left( s+\alpha ,2s \right),s\in \mathbb{C} \right\}$. It has simple theory, very close to that of the Asai L-function. It is an integral representation of the product $L\left( s+\alpha ,\pi \right)L\left( 2s,{{\Lambda }^{2}},\pi \right)$, which we denote by ${{L}^{\operatorname{lin}}}\left( s,\pi ,\alpha \right)$ for this abstract, when $\pi$ is a cuspidal automorphic representation of $GL\left( k,\mathbb{A} \right)$ for $\mathbb{A}$ the adeles of a number field. When $k$ is even, we show that the partial $L$-function ${{L}^{\text{lin,S}}}\left( s,\text{ }\!\!\pi\!\!\text{ ,}\alpha \right)$ has a pole at $1/2$ if and only if $\pi$ admits a (twisted) global period. This gives a more direct proof of a theorem of Jacquet and Friedberg, asserting that π has a twisted global period if and only if $L\left( \alpha +1/2,\text{ }\!\!\pi\!\!\text{ } \right)\ne 0$ and $L\left( 1,{{\Lambda }^{2}},\pi \right)=\infty $. When $k$ is odd, the partial $L$-function is holmorphic in a neighbourhood of $\operatorname{Re}\left( s \right)\ge 1/2$ when $\operatorname{Re}\left( \alpha \right)\,\,\text{is}\,\,\ge \text{0}\,$.

It is well known that a discrete group that is both amenable and has Kazhdan’s Property $T$ must be finite. In this note we generalize this statement to the case of transformation groups. We show that if $G$ is a discrete amenable group acting on a compact Hausdorff space $X$, then the transformation group ${{C}^{*}}$-algebra ${{C}^{*}}\left( X,\,G \right)$ has Property $T$ if and only if both $X$ and $G$ are finite. Our approach does not rely on the use of tracial states on ${{C}^{*}}\left( X,\,G \right)$.

The cover product of disjoint graphs $G$ and $H$ with fixed vertex covers $C\left( G \right)$ and $C\left( H \right)$, is the graph $G\circledast H$ with vertex set $V\left( G \right)\cup V\left( H \right)$ and edge set

$$E\left( G \right)\,\cup \,E\left( H \right)\,\cup \,\left\{ \left\{ i,\,j \right\}\,:\,i\,\in \,C\left( G \right),\,j\,\in \,C\left( H \right) \right\}.$$

We describe the graded Betti numbers of $G\circledast H$ in terms of those of $G$ and $H$. As applications we obtain: (i) For any positive integer k there exists a connected bipartite graph $G$ such that $\text{reg}\,R/I\left( G \right)\,=\,{{\mu }_{s}}\left( G \right)\,+\,k$, where, $I\left( G \right)$ denotes the edge ideal of $G$, $\text{reg}\,\text{R/I}\left( G \right)$ is the Castelnuovo–Mumford regularity of $\text{R/I}\left( G \right)$ and ${{\mu }_{s}}\left( G \right)$ is the induced or strong matching number of $G$; (ii)The graded Betti numbers of the complement of a tree depends only upon its number of vertices; (iii)The $h$-vector of $R/I\left( G\circledast H \right)$ is described in terms of the $h$-vectors of $\text{R/I}\left( G \right)$ and $R/I\left( H \right)$. Furthermore, in a different direction, we give a recursive formula for the graded Betti numbers of chordal bipartite graphs.

We consider the class of polynomial differential systems of the form $\dot{x} =\,\lambda x\,-\,y\,+\,{{P}_{n}}\left( x,\,y \right)$ , $\dot{y} =\,x\,+\,\lambda y\,+\,{{Q}_{n}}\left( x,\,y \right)$ where ${{P}_{n}}$ and ${{Q}_{n}}$ are homogeneous polynomials of degree $n$ . For this class of differential systems we summarize the known results for the existence of limit cycles, and we provide new results for their nonexistence and existence.

Inspired by the invariant of a number field given by its zeta function, we define the notion of weak arithmetic equivalence and show that under certain ramification hypotheses this equivalence determines the local root numbers of the number field. This is analogous to a result of Rohrlich on the local root numbers of a rational elliptic curve. Additionally, we prove that for tame non-totally real number fields, the integral trace form is invariant under arithmetic equivalence

We show that for a coanalytic subspace $X$ of ${{2}^{\omega }}$, the countable dense homogeneity of ${{X}^{\omega }}$ is equivalent to $X$ being Polish. This strengthens a result of Hrušák and Zamora Avilés. Then, inspired by results of Hernández-Gutiérrez, Hrušák, and van Mill, using a technique of Medvedev, we construct a non-Polish subspace $X$ of ${{2}^{\omega }}$ such that ${{X}^{\omega }}$ is countable dense homogeneous. This gives the first $\text{ZFC}$ answer to a question of Hrušák and Zamora Avilés. Furthermore, since our example is consistently analytic, the equivalence result mentioned above is sharp. Our results also answer a question of Medini and Milovich. Finally, we show that if every countable subset of a zero-dimensional separable metrizable space $X$ is included in a Polish subspace of $X$, then ${{X}^{\omega }}$ is countable dense homogeneous.

One can easily show that any meromorphic function on a complex closed Riemann surface can be represented as a composition of a birational map of this surface to $\mathbb{C}{{\mathbb{P}}^{2}}$ and a projection of the image curve froman appropriate point $p\in \mathbb{C}{{\mathbb{P}}^{2}}$ to the pencil of lines through $p$ . We introduce a natural stratification of Hurwitz spaces according to the minimal degree of a plane curve such that a given meromorphic function can be represented in the above way and calculate the dimensions of these strata. We observe that they are closely related to a family of Severi varieties studied earlier by J. Harris, Z. Ran, and I. Tyomkin.

Let $Q$ be a finite acyclic quiver, let $J$ be an ideal of $kQ$ generated by all arrows in $Q$, and let $A$ be a finite-dimensional $k$ -algebra. The category of all finite-dimensional representations of $\left( Q,\,{{J}^{2}} \right)$ over $A$ is denoted by $\text{rep}\left( Q,\,{{J}^{2}},\,A \right)$ . In this paper, we introduce the category $\text{exa}\left( Q,{{J}^{2}},A \right),$ which is a subcategory of $\text{rep}\left( Q,\,{{J}^{2}},\,A \right)$ of all exact representations. The main result of this paper explicitly describes the Gorenstein-projective representations in $\text{rep}\left( Q,\,{{J}^{2}},\,A \right)$, via the exact representations plus an extra condition. As a corollary, $A$ is a self-injective algebra if and only if the Gorenstein-projective representations are exactly the exact representations of $\left( Q,\,{{J}^{2}} \right)$ over $A$.

We prove the non-existence of Hopf real hypersurfaces in complex two-plane Grassmannians with harmonic curvature with respect to the generalized Tanaka–Webster connection if they satisfy some further conditions.

We recently introduced a weighted Banach algebra $\mathcal{A}_{G}^{n}$ of functions that are holomorphic on the unit disc $\mathbb{D}$, continuous up to the boundary, and of the class ${{C}^{\left( n \right)}}$ at all points where the function $G$ does not vanish. Here, $G$ refers to a function of the disc algebra without zeros on $\mathbb{D}$. Then we proved that all closed ideals in $\mathcal{A}_{G}^{n}$ with at most countable hull are standard. In this paper, on the assumption that $G$ is an outer function in ${{C}^{\left( n \right)}}\,\left( {\bar{\mathbb{D}}} \right)$ having infinite roots in $\mathcal{A}_{G}^{n}$ and countable zero set ${{h}_{o}}\left( G \right)$, we show that all the closed ideals $I$ with hull containing ${{h}_{o}}\left( G \right)$ are standard.

For the Bergman projection operator $P$ we prove that

$$\left\| P:\,{{L}^{1}}\left( B,\,d\lambda \right)\,\to \,{{B}_{1}} \right\|\,=\,\frac{\left( 2n\,+\,1 \right)!}{n!}.$$

Here $\lambda$ stands for the hyperbolic metric in the unit ball $B$ of ${{\mathbb{C}}^{n}}$, and ${{B}_{1}}$ denotes the Besov space with an adequate semi-norm. We also consider a generalization of this result. This generalizes some recent results due to Perälä.

Necessary and sufficient conditions are given for the existence of a graph decomposition of the Kneser Graph $K{{G}_{n,2}}$ and of the Generalized Kneser Graph $GK{{G}_{n,3,1}}$ into paths of length three.