We use the concept of outwardly simple line families (see Hammer and Sobczyk (4)) first to obtain conditions involving mid-chords that ensure that a plane convex set is centro-symmetric, and secondly to show that it is possible to inscribe a semicircle of diameter ω in any convex set of minimal width ω in at least 3 different ways. We show that a plane convex set X is centro-symmetric if every mid-chord of X (that is every chord of X mid-way between two parallel lines of support of X) bisects the area of X, or alternatively if every mid-chord of X is a diameter of X (that is a longest chord in some direction). Hammer and Smith (3) have used outwardly simple line families in a different way to show that a plane convex set X is centro-symmetric if every diameter of X bisects the area of X, or if every diameter of X bisects the perimeter of X.

Suppose that

is regular in the unit disk D = {|z| < 1}, and assumes there values ω lying in a domain Δ. It is natural to ask what effect this restriction has on the coefficients aν. The strongest order result we can hope to prove is that

A Banach space X is said to have the Banach–Saks property (BS) if every bounded sequence (xn) in X has a subsequence (), which is (C, 1) convergent in norm to a point x in X; that is,

Kakutani (7) showed that all uniformly convex spaces are (BS); moreover, all (BS) spaces are reflexive. It is further known that both these implicationsare strict: see, for example, Baernstein (1) and Diestel (4).

A unital JB-algebra is a Jordan algebra A with identity together with a complete norm satisfying, for all a, b ∈ A,

(i) (a2b) a = a2(ba),

(ii) ∥a2∥ = ∥a∥2,

(iii) ∥ab∥ ≤ ∥a∥ ∥b∥,

(iv) ∥a2 + b2∥ ≥ ∥a2∥, ∥b2∥.

(It should be noted that axiom (iii) is a consequence of (ii) and (iv).) Such spaces have been studied by several authors (3, 6, 11), and as a consequence their structure is now quite well understood. Many of the results of these papers, while relying on the existence of an identity for their proofs, can be formulated for algebras which lack this property. C*-algebra theory and operator theory abound in examples of spaces which fail to be unital JB-algebras only in this one respect, and this motivates the study of the general case undertaken in this note.

In this paper every space will be 2-local, for example BO will mean the 2-localization of the space usually denoted BO.

The crucial step in the proof of the Topological Stability Theorem is the construction of a certain contact-invariant Whitney stratification of the sufficient jets in the jet space Jk(n, p). There is therefore a certain intrinsic interest in the construction of natural contact-invariant Whitney stratifications of the jet space. It has long been known that if there are only finitely many contact orbits then these provide a Whitney stratification, but in general there is the double problem of finding a candidate for a Whitney stratification, and then establishing that it has the desired properties. Virtually nothing is known about this problem, so it seems sensible to start by attempting to understand the first non-trivial examples which arise. Since functions are rather better understood than mappings it seems natural to try the case p = 1 first. The complexity of the problem now increases with k. When k = 1, 2 there are only finitely many contact orbits, so we start with k = 3. Having fixed p = 1, k = 3 we turn our attention to n. When n = 1, 2 we still obtain only finitely many contact orbits, as easy computations verify, so we start with n = 3. Thus our first example is J3(3, 1). It is a relatively easy matter to list the contact orbits in this case, and in so doing one is presented with an obvious candidate for a Whitney stratification. Our objective is to show that this candidate is indeed a Whitney stratification.

Let S be both a topological space and a semigroup. For s ∈ S, define the maps λs and ρs of S to S by

We shall say that S is a right-topological (resp. left-topological) semigroup if ρs (resp. λs) is continuous for each s in S. We denote by Λ(S) the set

this is a subsemigroup of S.

Let A and G be locally compact groups and α a continuous action of G on A, and let denote the semi-direct product of A and G. Then we prove that the left Hilbert algebra of continuous functions with compact support, has the same achieved left Hilbert algebra, as the crossed product of K(A)" by the associated action α̃ of G on . As a consequence we obtain that the canonical weight on is the dual weight of the canonical weight on K(A)".

A bilinear map ø Ra x Rb → Rc is non-singular if ø (x, y) = 0 implies x = 0 or y = 0. For background information on such maps see (4, 5, 6, 14). If we apply the ‘Hopf construction’ to ø, we get a map

defined by 2ø(x, y)) for all x ∈ Ra, y ∈ Rb satisfying ∥x∥2 + ∥y∥2 = 1. Homotopically, Jø coincides with the map obtained by first restricting and normalizing ø to , and then applying the standard Hopf construction ((13), p. 112). In any case, one gets an element [Jø] in , which in turn determines a stable homotopy class of spheres {Jø} in the d-stem , where d = a + b − c −1. An element in which equals {Jø} for some non-singular bilinear map ø will be called bilinearly representable. The first purpose of this paper is to prove

A globally convergent algorithm is presented for the total, or partial, factorization of a polynomial. Firstly, a circle is found containing all the zeros. Secondly, a search procedure locates smaller circles, each containing a zero, and the multiplicities are then calculated. Thirdly, a simultaneous Iteration Function is used to accelerate convergence. The Iteration Function is chosen from a class of such functions derived herein to deal with the general case of multiple zeros; various properties of these functions are also discussed. Finally, sample numerical results are given which demon-strate the effectiveness of the algorithm.

Let {Xnj, 1 ≤ j ≤ kn} be independent random variables with zero means and satisfying . Let p ≥ 1. We prove that

if and only if, for all ε > 0,

and we use this result to obtain necessary and sufficient conditions for the Lp convergence of sums of non-negative, independent random variables.

A conjecture of Cox and Isham about the asymptotic form of the covariance of counts in two counters, linked by a partially shared input, is established by means of Smith's theory of cumulative processes and a variant of Wald's identity.

A form of the Hopf bifurcation theorem specially suited to systems in block-diagram form has been developed, which allows one to deal with high or infinite order linear elements solely in terms of their transfer functions. The results are proved by the method of harmonic balance, and, for general non-linear systems, lead to criteria for the existence and stability of bifurcated orbits generalizing those derived by various authors for systems of ordinary differential equations. In the particular case of control loops with a single non-linearity, a simple addition to the Nyquist diagram of the loop determines the amplitude and frequency of bifurcated orbits, and whether they occur when the equilibrium is stable or unstable. The analysis is independent of the central manifold theorem, and of Floquet theory.

The Hopf bifurcation theorem describes the creation of a limit cycle from an isolated singular point of a system of first-order differential equations depending on a parameter. This paper describes a method for determining explicitly a range of values of the parameter throughout which the Hopf configuration continues to exist; only the three-dimensional case is described in this paper, but the method can be generalized.

A deeper mathematical insight into physical problems is gained when a relatively elementary problem is generalized mathematically beyond the bounds of physical reality, particularly when the results are independent of the generalization. See, for example, Heading (3).

Bernstein's theorem states that the only complete minimal graphs in R3 are the hyperplanes. We shall produce evidence in favour of some conjectural generalizations of this theorem for the cases of spacelike hypersurfaces of constant mean curvature in Minkowski space and in de Sitter space. The results suggest that the class of asymptotically simple space-times admitting a complete spacelike hypersurface of constant mean curvature may well be considerably smaller than the general class of asymptotically simple space-times.

Zeeman has drawn attention to the sequences in which catastrophes, or modes of instability, can be linked, and it is a common observation that sequences of catastrophes of low order are always found in the environment of catastrophes of higher order. In this paper, a simple buckling model is presented that generates in an elegant manner a complete sequence of the umbilic catastrophes as represented by the semi-symmetric branching points. The scan of a single fundamental parameter of this model is shown to trace a route through all regimes of the umbilic bracelet, giving in turn the hyperbolic, symbolic, elliptic, parabolic and hyperbolic umbilic catastrophes.