The theory of two-dimensional anisotropic dielectrics is developed using complex variable methods, and the problems of an elliptic cylinder in a uniform electric field and of a line charge before a dielectric plane and circular cylinder are then discussed. The method is believed to be more general than that given by Netushil [1].

In this paper we shall set out the generalization, for n-dimensional space Sn, of some recent results about complete quadrics and complete collineations in S2, S3 and S4. For the results about complete conies in S2, originally introduced by Study [1], we refer the reader to papers by Severi ([2], [3]), van der Waerden [4], Semple [5]; for those about complete quadrics in S3, to Semple ([6], [7]); for the extension to S4 to Alguneid [8]; for the general concept of complete collineations in Sn, and for results in S2 and S3, to Semple [9].

In [3] Pontrjagin proved the following form of the Alexander duality theorem:

Theorem A. Let K be a sub-polyhedron of the n–dimensional sphere, Sn. Let G, G* be orthogonal topological groups, G being compact. Then Hr(K; G) and Hn–r–1(Sn–K; G*) are orthogonal with the product of αεHr(K; G) and αεHn−r−1(SnK; G) determined as the linking coefficientof some cycle of class a with some cycle of class α

Various attempts have been made to identify the slip lines or Lüder lines which are observed in solids with surfaces of discontinuity or characteristic surfaces associated with solutions of equations of plasticity. Results such as those obtained in [1], together with the observed fact that such lines occur in a variety of types of experiments, indicate that, for two well-known theories of plasticity, characteristic surfaces fail to exist in situations in which such lines are observed. This can come about in two ways, one being that real characteristic directions do not exist, the other being that they do, but that the characteristic surface elements do not unite to form surfaces. The latter situation seems to arise from the fact that, even in truly three-dimensional problems, the equations considered admit only a finite number of characteristic directions. Results such as those given in [2] indicate that, if real characteristic directions do not always exist, there is some doubt as to whether one can identify such lines with surfaces of discontinuity. Another point to be considered is the ease with which solutions may be obtained. For equations possessing real characteristics, the method of characteristics is a powerful tool to use in solving two-dimensional problems. It is noted in [3], Ch. X, that, in axially symmetric problems, one cannot use this method to obtain solutions of the von Mises equations. In treating such problems, it may be easier to use equations which appear to be more complicated, but which possess real characteristics. These facts suggest that plasticity equations which always possess real characteristic directions are to be preferred to those which do not. Some workers in plasticity appreciate this, as is indicated by remarks made in [4]. However, no one has taken a rather general theory of plasticity, such as the theory of perfectly plastic solids, and attempted to determine which of the equations included in it have this property. We made an unsuccessful attempt to do so for a theory which is roughly equivalent. The purpose of this paper is to present this theory, to indicate the basic mathematical problem involved, and to record a partial solution of it.

It is well known that the star domain

in the plane is boundedly reducible, that is, it contains a bounded star body with the same lattice determinant, namely √5. Hence the bounded star domain

has the same lattice determinant as K has if r is sufficiently large. The following result is therefore perhaps a little surprising.

The following well-known conjecture is generally attributed to Minkowski:

Let L1, …, Ln be n real homogeneous linear forms of determinant Δ ≠ 0 in the n variables x1, …, xn; and let (x1′, …, xn′) be any point. Then there exists a point (x1, xn) congruent to (x1′, …, xn′) (mod 1) at which

If a group G is presented in terms of generators and relations, then the classical Reidemeister-Schreier Theorem [1] gives a presentation for any subgroup of G. If G is a free product of groups Gα each of which is presented in terms of generators and relations, then the main result of this paper is a presentation for any subgroup H of G, which shows the nature of H as a free product of certain subgroups of G. This result is a generalization of the celebrated Kuroš Theorem [2]. It also includes the Reidemeister–Schreier Theorem and the Schreier Theorem [1] which states that any subgroup of a free group is free.

The analysis of the intervals which arise between events occurring randomly in time is a problem which is both interesting and important statistically. Two distinct types of data may arise: either the period of time during which the events are observed may be fixed or the number of intervals may be fixed. It may happen that the intervals between pairs of events, close in time, cannot be accurately measured. It is thus necessary to consider the lengths of intervals ordered according to their magnitudes. We derive here functions of these ordered interval lengths which may be used as a basis for tests for randomness of events occurring in a fixed period of time. The mathematical formulation of this problem is in terms of the classical problem of intervals between points on a line.

The idea of a geometry in which the coordinates are elements of a linear algebra, instead of the conventional field, goes back to C. Segre. Most of the subsequent work seems to have been done by N. Spampinato who developed some general results and applied them particularly to the case of an algebra of dual numbers defined over the complex field; in general, his aim appears to have been the study of algebraic varieties in the new kind of space.

On page 2 of my paper “Rational approximations to algebraic numbers” [Mathematika 2 (1955), 1–20], I referred to possible generalizations of my theorem, and mentioned that I had proved the following:

Let α be any algebraic number, not rational. If the inequality

is satisfied by infinitely many algebraic numbers β of degree g, then κ ≤ 2g.

Two finite real functions ƒ(x) and g(x), defined for — ∞ < x < ∞, are said to be Riemann equivalent if |ƒ(x)—g(x)| has a zero Riemann integral over every finite interval; we then write ƒ~g or

N. G. de Bruijn conjectured that if ƒ(x+h)~ƒ(x) for every real number h, then ƒ~c where c is a constant; this was proved by P. Erdös [1]. In this note we associate with an arbitrary function ƒ the additive group (ƒ) of all numbers h which make ƒ(x)~ƒ(x+h), i.e. which make

In a recent book, L. H. Loomis has obtained the “Bohr compactification” of a topological group, in terms of almost periodic functions, by applying the representation theory of commutative B-algebras. It is simpler, and perhaps more natural, to consider this matter from the point of view of comparative topology; we can then obtain a more general result, in that the discussion is no longer restricted to the case of numerically valued (or even vector-valued) functions.

Consider a set of n points lying in a square of side 1. Verblunsky has shown that, if n is sufficiently large, there is some path through all n points whose length does not exceed (2·8n)1/2+2. L. Fejes Tóth has drawn attention to the case when the n points consist of all points of a regular hexagonal lattice lying in the unit square, in which case the length of the shortest path is easily seen to be asymptotically equal to

The main case of Siegel's theorem on algebraic curves may be stated as follows:

THEOREM 1. Let

be an irreducible algebraic curve of genus g≥1, ƒ(x, y) being a polynomial with algebraic coefficients. Let K be an algebraic field of finite degree over the rational field; let o be the ring of integers in K; and let j be a positive rational integer. Then there are at most finitely many points (x, y) on ℭ for which jxεο and yεK.

Let →(X) be a function of the n variables (X) = (X1, …, Xn) defined for all real (X). A fundamental problem in the theory of Diophantine approximation is to prove the existence of real numbers (X) ≡ (x) (mod 1), where (x) = (x1, …, xn) is any given set of real numbers, for which

In several of his papers, Mordell has developed a method which, in certain cases, leads to an inequality connecting the critical determinant of an n dimensional star body with that of a related n—1 dimensional star body. The purpose of this paper is to exhibit the underlying principle in a general form and to show that the same principle can sometimes be carried further.

The method devised by Hardy and Littlewood for the solution of Waring's Problem, and further developed by Vinogradov, applies quite generally to Diophantine equations of an additive type. One particular result that can be proved by this method is that if a1, …, as are integers not all of the same sign, and if s is greater than a certain number depending only on k, the Diophantine equation

has infinitely many solutions in positive integers x1, …, xs, provided that the corresponding congruence has a non-zero solution to every prime power modulus. A result of a similar kind holds if on the right of (1) there stands an arbitrary integer in place of 0.