It is proved that every space L2 (I1, ∪ I2), where I1 and I2 are finite intervals, has a Riesz basis of complex exponentials , {λk} a sequence of real numbers. A partial result for the corresponding problem for n≧3 finite intervals is also obtained.

The Dirichlet problem for the Laplace equation in a connected-plane region with cuts is studied. The existence of a classical solution is proved by potential theory. The problem is reduced to a Fredholm equation of the second kind, which is uniquely solvable.

A squareroot of an ambiguous form in the principal genus of primitive integral binary quadratic forms of fixed discriminant is given explicitly in terms of a solution of a certain Legendre equation.

In his fundamental paper (3), Thorn proved, among other things, that a mod-2 homology class of an n-dimensional, closed, compact, C∞ manifold, which has dimension n/2, can be realised by a submanifold, (see (3), Théorème II. 1 and Corollaire 11.13).

In this note we examine the question of realisability of mod-2 homology classes of the next higher dimension.

Let {pn} be a positive sequence. The Nörlund transformation (N, pn) maps the sequence {Sn} into the sequence {tn} by means of the equation

where

In this paper, we study the boundary-initial value problem for a linear elastic body ina bounded domain, when the body force depends on the displacement vector u in asublinear way.

Recently, much attention has been given to nonlinear body forces not only to studythe fundamental solutions of the equations governing linear elastodynamics, see e.g.Kecs [3], but also to derive global non existence results in abstract problems with directapplications to nonlinear heat diffusion or to the nonlinear wave equation, see e.g. Ball[1], Levine and Payne [10].

Let G be a non-discrete LCA group with dual group Γ. Denote by M(G) the usual convolution algebra of bounded Borel measures on G and Ma(G) those μ ∈ M(G) which are absolutely continuous with respect to mG—the Haar measure on G.

If a is an element of a complex unital Banach algebra whose numerical range is confined to a closed angular region with vertex at zero and angle strictly less than π, we imbed a in a holomorphic semigroup with parameter in the open right half plane.

There has been recently a great development in the theory of semigroups in Banach algebras (see [6]), with attention focused on the relation between the structure of a given Banach algebra and the existence of continuous or holomorphic non-trivial semigroups with certain properties with range in this algebra. The interest of this paper arises from the fact that we relate in it, we think for the first time, this new point of view in the theory of Banach algebras with the already classic one of numerical ranges [2,3]. The proofs of our results use, in addition to some basic ideas from numerical ranges in Banach algebras, the concept of extremal algebra Ea(K) of a compact convex set K in ℂ due to Bollobas [1] and concretely the realization of Ea(K) achieved by Crabb, Duncan and McGregor [4].

We define a new height function $\mathcal{R}(\alpha)$, the Remak height of an algebraic number $\alpha$. We give sharp upper and lower bounds for $\mathcal{R}(\alpha)$ in terms of the classical Mahler measure $M(\alpha)$. Study of when one of these bounds is exact leads us to consideration of conjugate sets of algebraic numbers of norm $\pm 1$ lying on two circles centred at 0. We give a complete characterization of such conjugate sets. They turn out to be of two types: one related to certain cubic algebraic numbers, and the other related to a non-integer generalization of Salem numbers which we call extended Salem numbers.

AMS 2000 Mathematics subject classification: Primary 11R06

The class of non-metacyclic finite soluble groups known to have 2-generator 2-relation presentations is small. Classes of such groups are given in (3), (4), (8) and (9). Some subclasses of the groups discussed in (1) and (2) also provide examples, while a class of finite nilpotent 2-generator 2-relation groups is given by Macdonald in (7).

In a recent paper Mr J. M. Whittaker has given the following Theorem:—

If ψ (x) be the indefinite Riemann integral of a bounded positive function g(x), and if f(x) be any bounded function, then the equation

is true whenever either side exists.