Lie algebras graded by finite reduced root systems have been classified up to isomorphism. In this paper we describe the derivation algebras of these Lie algebras and determine when they possess invariant bilinear forms. The results which we develop to do this are much more general and apply to Lie algebras that are completely reducible with respect to the adjoint action of a finite-dimensional subalgebra.

Etant donnée une partie $D$ dénombrable et dense de $\mathbb{R}$, nous construisons une infinité de fonctions Lipschitziennes définies sur $\mathbb{R}$, s'annulant en zéro, dont le sous-différentiel proximal est égal à ]–1, 1[ en tout point de $D$ et est vide en tout point du complémentaire de $D$. Nous déduisons que deux fonctions dont la différence n'est pas constante peuvent avoir les mêmes sous-différentiels.

Central to the study of simple infinite dimensional $g\ell (n,\,\mathbb{C})$-modules having finite dimensional weight spaces are the torsion free modules. All degree 1 torsion free modules are known. Torsion free modules of arbitrary degree can be constructed by tensoring torsion free modules of degree 1 with finite dimensional simple modules. In this paper, the central characters of such a tensor product module are shown to be given by a Pieri-like formula, complete reducibility is established when these central characters are distinct and an example is presented illustrating the existence of a nonsimple indecomposable submodule when these characters are not distinct.

Let $G$ be a free product of cyclic groups of prime order. The structure of the unit group $U(\mathbb{Q}G)$ of the rational group ring $\mathbb{Q}G$ is given in terms of free products and amalgamated free products of groups. As an application, all finite subgroups of $U(\mathbb{Q}G)$, up to conjugacy, are described and the Zassenhaus Conjecture for finite subgroups in $\mathbb{Z}G$ is proved. A strong version of the Tits Alternative for $U(\mathbb{Q}G)$ is obtained as a corollary of the structural result.

Examples of simple, separable, unital, purely infinite ${{C}^{*}}$-algebras are constructed, including:

1. (1) some that are not approximately divisible;

2. (2) those that arise as crossed products of any of a certain class of ${{C}^{*}}$-algebras by any of a certain class of non–unital endomorphisms;

3. (3) those that arise as reduced free products of pairs of ${{C}^{*}}$-algebras with respect to any from a certain class of states.

The notion of shape fibration with the near lifting of near multivalued paths property is studied. The relation of these maps—which agree with shape fibrations having totally disconnected fibers—with Hurewicz fibrations with the unique path lifting property is completely settled. Some results concerning homotopy and shape groups are presented for shape fibrations with the near lifting of near multivalued paths property. It is shown that for this class of shape fibrations the existence of liftings of a fine multivalued map is equivalent to an algebraic problem relative to the homotopy, shape or strong shape groups associated.

The universal enveloping algebra, $U(\mathfrak{g})$, of a Lie algebra $\mathfrak{g}$ supports some norms and seminorms that have arisen naturally in the context of heat kernel analysis on Lie groups. These norms and seminorms are investigated here from an algebraic viewpoint. It is shown that the norms corresponding to heat kernels on the associated Lie groups decompose as product norms under the natural isomorphism $U({{\mathfrak{g}}_{1\,}}\oplus \,{{\mathfrak{g}}_{2}})\,\cong \,U({{\mathfrak{g}}_{1}})\,\otimes \,U({{\mathfrak{g}}_{2}})$. The seminorms corresponding to Green's functions are examined at a purely Lie algebra level for $\text{sl(2,}\,\mathbb{C}\text{)}$. It is also shown that the algebraic dual space ${U}'$ is spanned by its finite rank elements if and only if $\mathfrak{g}$ is nilpotent.

We show that every equivariant polynomial automorphism of a $\Theta $- representation and of the reduction of an irreducible $\Theta $-representation is a multiple of the identity.

In this paper, we first show that the central height of the unit group of the integral group ring of a periodic group is at most 2. We then give a complete characterization of the $n$-centre of that unit group. The $n$-centre of the unit group is either the centre or the second centre (for $n\,\ge \,2$).

For the $q$-series $\sum\nolimits_{n=0}^{\infty }{{{a}^{n}}{{q}^{b{{n}^{2}}+cn}}/}\,{{(q)}_{n}}$ we construct a companion $q$-series such that the asymptotic expansions of their logarithms as $q\,\to \,{{1}^{-}}$ differ only in the dominant few terms. The asymptotic expansion of their quotient then has a simple closed form; this gives rise to a new $q$–hypergeometric identity. We give an asymptotic expansion of a general class of $q$-series containing some of Ramanujan's mock theta functions and Selberg's identities.

The regular star-polyhedron $\left\{ 5,\,\frac{5}{2} \right\}$ is isomorphic to the abstract polyhedron $\left\{ 5,\,5|3 \right\}$, where the last entry “3” in its symbol denotes the size of a hole, given by the imposition of a certain extra relation on the group of the hyperbolic honeycomb $\left\{ 5,\,5 \right\}$. Here, analogous formulations are found for the groups of the regular 4-dimensional star-polytopes, and for those of the non-discrete regular 4-dimensional honeycombs. In all cases, the extra group relations to be imposed on the corresponding Coxeter groups are those arising from “deep holes”; thus the abstract description of $\left\{ 5,\,{{3}^{k}},\,\frac{5}{2} \right\}\,\text{is}\,\left\{ 5,\,{{3}^{k}},\,5|3 \right\}\,\text{for}\,k\,=\,1\,\text{or}\,\text{2}$. The non-discrete quasi-regular honeycombs in ${{\mathbb{E}}^{3}}$, on the other hand, are not determined in an analogous way.