A class of Toeplitz type operators acting on the weighted Bergman spaces of the unit ball in the $n$-dimensional complex space is considered and two pluriharmonic symbols of commuting Toeplitz type operators are completely characterized.

In a paper [1], published in 1990, in a (somewhat inaccessible) conference proceedings, the authors had shown that for the unitary operators on a separable Hilbert space, endowed with the strong operator topology, those with singular, continuous, simple spectrum, with full support, forma dense ${{G}_{\delta }}$. A similar theorem for bounded self-adjoint operators with a given normbound (omitting simplicity) was recently given by Barry Simon [2], [3], with a totally different proof. In this note we show that a slight modification of our argument, combined with the Cayley transform, gives a proof of Simon’s result, with simplicity of the spectrum added.

A new class of homology groups associated to a 3-manifold is defined. The theories measure the syzygies between skein relations in a skein module. We investigate some of the properties of the homology theory associated to the Kauffman bracket.

It is shown that if a Banach space $X$ admits a ${{C}^{k}}$-smooth bump function, and ${{X}^{*}}$ is Asplund, then $X$ admits ${{C}^{k}}$-smooth partitions of unity.

If $F$ and ${F}'$ are free $R$-modules, then $M\cong F/H$ and $M\,\cong \,{F}'\,/\,{H}'$ are viewed as equivalent presentations of the $R$-module $M$ if there is an isomorphism $F\,\to \,{F}'$ which carries the submodule $H$ onto ${H}'$. We study when presentations of modules of projective dimension 1 over Prüfer domains of finite character are necessarily equivalent.

In the present paper we consider the problem of finding power integral bases in number fields which are composits of two subfields with coprime discriminants. Especially, we consider imaginary quadratic extensions of totally real cyclic number fields of prime degree. As an example we solve the index form equation completely in a two parametric family of fields of degree 10 of this type.

In Bernoulli site percolation on Penrose tilings there are two natural definitions of the critical probability. This paper shows that they are equal on almost all Penrose tilings. It also shows that for almost all Penrose tilings the number of infinite clusters is almost surely 0 or 1. The results generalize to percolation on a large class of aperiodic tilings in arbitrary dimension, to percolation on ergodic subgraphs of ${{\mathbb{Z}}^{d}}$, and to other percolation processes, including Bernoulli bond percolation.

A theory of minimal realizations of rational matrix functions $W(\lambda )$ in the “pencil” form $W(\lambda )=C{{(\lambda {{A}_{1}}-{{A}_{2}})}^{-1}}B$ is developed. In particular, properties of the pencil $\text{ }\!\!\lambda\!\!\text{ }{{A}_{1}}\,-\,{{A}_{2}}$ are discussed when $W(\lambda )$ is hermitian on the real line, and when $W(\lambda )$ is hermitian on the unit circle.

The aim of this article is to obtain an upper bound for the exponential sums $\sum{e(f(x)\,/\,q)}$, where the summation runs from $x=1$ to $x=q$ with $(x,q)=1$ and $e(\alpha )$ denotes $\exp (2\pi i\alpha )$.

We shall show that the upper bound depends only on the values of $q$ and $s$, where $s$ is the number of terms in the polynomial $f(x)$.

The spectra of the Toeplitz operators on the weighted Hardy space ${{H}^{2}}\,(W\,d\theta \,/\,2\pi )$ and the Hardy space ${{H}^{p}}\,(d\theta \,/\,2\pi )$, and the singular integral operators on the Lebesgue space ${{L}^{2}}\,(d\theta \,/\,2\pi )$ are studied. For example, the theorems of Brown-Halmos type and Hartman-Wintner type are studied.

A new oscillation criterion is given for the delay differential equation ${x}'\,(t)\,+\,p(t)x\,(t\,-\,\text{ }\!\!\tau\!\!\text{ (t)})\,=\,0$, where $p,\,\text{ }\!\!\tau\!\!\text{ }\,\in \,\text{C}\,\text{( }\!\![\!\!\text{ 0,}\,\infty ),\,\text{ }\!\![\!\!\text{ 0,}\,\infty )\text{)}$ and the function $T$ defined by $T(t)\,=\,t-\,\text{ }\!\!\tau\!\!\text{ }\,\text{(t),}\,\text{t}\ge \,\text{0}$ is increasing and such that ${{\lim }_{t\to \infty }}\,T(t)\,=\,\infty $. This criterion concerns the case where $\lim \,{{\inf }_{t\to \infty }}\int _{T(t)}^{t}p(s)ds\le \frac{1}{e}$.

For two functions $f$ and $g$, define $g\ll f$ to mean that $g$ satisfies every algebraic differential equation over the constants satisfied by $f$. The order $\ll $ was introduced in one of a set of problems on algebraic differential equations given by the late Lee Rubel. Here we characterise the set of $g$ such that $g\ll f$, when $f$ is a given Liouvillian function.

Various authors have studied when a Banach space can be renormed so that every weakly compact convex, or less restrictively every compact convex set is an intersection of balls. We first observe that each Banach space can be renormed so that every weakly compact convex set is an intersection of balls, and then we introduce and study properties that are slightly stronger than the preceding two properties respectively.

The growth series of compact hyperbolic Coxeter groups with 4 and 5 generators are explicitly calculated. The assertions of J. Cannon and Ph. Wagreich for the 4-generated groups, that the poles of the growth series lie on the unit circle, with the exception of a single real reciprocal pair of poles, are verified. We also verify that for the 5-generated groups, this phenomenon fails.

It is known that the Toeplitz algebra associated with any flow which is both minimal and uniquely ergodic always has a trivial ${{K}_{1}}$-group. We show in this note that if the unique ergodicity is dropped, then such ${{K}_{1}}$-group can be non-trivial. Therefore, in the general setting of minimal flows, even the $K$-theoretical index is not sufficient for the classification of Toeplitz operators which are invertible modulo the commutator ideal.

It is known that the product ${{\omega }_{1}}\times X$ of ${{\omega }_{1}}$ with an ${{M}_{1}}$-space may be non-normal. In this paper we prove that the product $\kappa \times X$ of an uncountable regular cardinal κ with a paracompact semi-stratifiable space is normal iff it is countably paracompact. We also give a sufficient condition under which the product of a normal space with a paracompact space is normal, from which many theorems involving such a product with a countably compact factor can be derived.

In this note we determine which dihedral subgroups of $\text{G}{{\text{L}}_{g}}\,(\mathbb{C})$ can be realized by group actions on Riemann surfaces of genus $g>1$.