For holomorphic functions $f$ in the unit disk $ \mathbb{D} $ with $f(0)= 0$, we prove a modulus growth bound involving the logarithmic capacity (transfinite diameter) of the image. We show that the pertinent extremal functions map the unit disk conformally onto the interior of an ellipse. We prove a modulus growth bound for elliptically schlicht functions in terms of the elliptic capacity ${\mathrm{d} }_{\mathrm{e} } f( \mathbb{D} )$ of the image. We also show that the function ${\mathrm{d} }_{\mathrm{e} } f(r \mathbb{D} )/ r$ is increasing for $0\lt r\lt 1$.

We obtain a fully explicit quantitative version of the Eisenstein theorem on algebraic power series which is more suitable for certain applications than the existing version due to Dwork, Robba, Schmidt and van der Poorten. We also treat ramified series and Laurent series, and we demonstrate some applications; for instance, we estimate the discriminant of the number field generated by the coefficients.

Let $K$ be a commutative ring with unity, $R$ an associative $K$-algebra of characteristic different from $2$ with unity element and no nonzero nil right ideal, and $f({x}_{1} , \ldots , {x}_{n} )$ a multilinear polynomial over $K$. Assume that, for all $x\in R$ and for all ${r}_{1} , \ldots , {r}_{n} \in R$ there exist integers $m= m(x, {r}_{1} , \ldots , {r}_{n} )\geq 1$ and $k= k(x, {r}_{1} , \ldots , {r}_{n} )\geq 1$ such that $\mathop{[{x}^{m} , f({r}_{1} , \ldots , {r}_{n} )] }\nolimits_{k} = 0$. We prove that: (1) if $\text{char} (R)= 0$ then $f({x}_{1} , \ldots , {x}_{n} )$ is central-valued on $R$; and (2) if $\text{char} (R)= p\gt 2$ and $f({x}_{1} , \ldots , {x}_{n} )$ is not a polynomial identity in $p\times p$ matrices of characteristic $p$, then $R$ satisfies ${s}_{n+ 2} ({x}_{1} , \ldots , {x}_{n+ 2} )$ and for any ${r}_{1} , \ldots , {r}_{n} \in R$ there exists $t= t({r}_{1} , \ldots , {r}_{n} )\geq 1$ such that ${f}^{{p}^{t} } ({r}_{1} , \ldots , {r}_{n} )\in Z(R)$, the center of $R$.

We show that every automorphism of a thick twin building interchanging the halves of the building maps some residue to an opposite one. Furthermore, we show that no automorphism of a locally finite 2-spherical twin building of rank at least 3 maps every residue of one fixed type to an opposite (a key step in the proof is showing that every duality of a thick finite projective plane admits an absolute point). Our results also hold for all finite irreducible spherical buildings of rank at least 3, and imply that every involution of a thick irreducible finite spherical building of rank at least 3 has a fixed residue.

Extreme points of compact, convex integral families of analytic functions are investigated. Knowledge about extreme points provides a valuable tool in the optimization of linear extremal problems. The functions studied are determined by a two-parameter collection of kernel functions integrated against measures on the torus. For specific choices of the parameters many families from classical geometric function theory are included. These families include the closed convex hull of the derivatives of normalized close-to-convex functions, the ratio of starlike functions of different orders, as well as many others. The main result introduces a surprising new class of extreme points.

Let $R$ be a commutative Noetherian ring, $M$ be a finitely generated $R$-module and $\mathfrak{a}$ be an ideal of $R$ such that $\mathfrak{a}M\not = M$. We show among the other things that, if $c$ is a nonnegative integer such that ${ H}_{\mathfrak{a}}^{i} (M)= 0$ for all $i\lt c$, then there is an isomorphism $\mathrm{End} ({ H}_{\mathfrak{a}}^{c} (M))\cong { \mathrm{Ext} }_{R}^{c} ({ H}_{\mathfrak{a}}^{c} (M), M)$; and if $c$ is a nonnegative integer such that ${ H}_{\mathfrak{a}}^{i} (M)= 0$ for all $i\not = c$, there are the following isomorphisms:

(i) $~\quad{ H}_{\mathfrak{b}}^{i} ({ H}_{\mathfrak{a}}^{c} (M))\cong { H}_{\mathfrak{b}}^{i+ c} (M)$ and

(ii) $\quad{ \mathrm{Ext} }_{R}^{i} (R/ \mathfrak{b}, { H}_{\mathfrak{a}}^{c} (M))\cong { \mathrm{Ext} }_{R}^{i+ c} (R/ \mathfrak{b}, M)$

for all $i\in { \mathbb{N} }_{0} $ and all ideals $\mathfrak{b}$ of $R$ with $\mathfrak{b}\supseteq \mathfrak{a}$. We also prove that if $\mathfrak{a}$ and $\mathfrak{b}$ are ideals of $R$ with $\mathfrak{b}\supseteq \mathfrak{a}$ and $c: = \mathrm{grade} (\mathfrak{a}, M)$, then there exists a natural homomorphism from $\mathrm{End} ({ H}_{\mathfrak{a}}^{c} (M))$ to $\mathrm{End} ({ H}_{\mathfrak{b}}^{c} (M))$, where $\mathrm{grade} (\mathfrak{a}, M)$ is the maximum length of $M$-sequences in $\mathfrak{a}$.

Paterson showed how to construct an étale groupoid from an inverse semigroup using ideas from functional analysis. This construction was later simplified by Lenz. We show that Lenz’s construction can itself be further simplified by using filters: the topological groupoid associated with an inverse semigroup is precisely a groupoid of filters. In addition, idempotent filters are closed inverse subsemigroups and so determine transitive representations by means of partial bijections. This connection between filters and representations by partial bijections is exploited to show how linear representations of inverse semigroups can be constructed from the groups occurring in the associated topological groupoid.

We give a negative answer to the question raised by Mart Abel about whether his proposed definition of ${K}_{0} $ and ${K}_{1} $ groups in terms of quasi multiplication is indeed equivalent to the established ones in algebraic $K$-theory.

We prove that when $(a, m)= 1$ and $a$ is a quadratic residue $\hspace{0.167em} \mathrm{mod} \hspace{0.167em} m$, there are infinitely many Carmichael numbers in the arithmetic progression $a\hspace{0.167em} \mathrm{mod} \hspace{0.167em} m$. Indeed the number of them up to $x$ is at least ${x}^{1/ 5} $ when $x$ is large enough (depending on $m$).

We characterize the abelian groups $G$ for which the functors $\mathrm{Ext} (G, - )$ or $\mathrm{Ext} (- , G)$ commute with or invert certain direct sums or direct products.