In this note it is shown that a contractive matrix selfmap T of l∞ has T2 a contraction; hence the techniques used in showing ITNC for lp(1 ≤ p < ∞), c0, and c do not apply to l∞.

In recent papers Brewer and Mott have studied integral domains which have finite character globally. This paper concentrates on domains which have finite character locally. Examples include global finite character domains plus Prufer, almost Dedekind, and almost Krull domains. General properties are given, including a valuation-theoretic characterization. The effect of requiring essential and/or rank one valuations is also studied.

Let X be a topological space and G a subgroup of the homeomorphism group H(X) with the topology of point-wise convergence. It is well-known that if X is uniformizable and G is equicontinuous with respect to a compatible uniformity then G is a topological group. In this paper we show that essentially this same result applies when X is only an R0-space (and hence in particular if X is T1 or regular). A corresponding result for regular spaces has been proved [2].

R. Arens and I. Kaplansky ([1]) call a ring A biregular if every two sided principal ideal of A is generated by a central idempotent and a ring A strongly regular if for any a in A there exists b in A such that a=a2b. In ([1], Sections 2 and 3), a lot of interesting properties of a biregular ring and a strongly regular ring are given. Some more properties can also be found in [3], [5], [8], [9] and [13]. For example, J. Dauns and K. Hofmann ([3]) show that a biregular ring A is isomorphic with the global sections of the sheaf of simple rings A/K where K are maximal ideals of A. The converse is also proved by R. Pierce ([9], Th. 11–1). Moreover, J. Lambek ([5], Th. 1) extends the above representation of a biregular ring to a symmetric module.

In this paper we generalize the concept of the Rayleigh quotient to a complex Banach space. Lord Rayleigh investigated the quotient

(1)

considered as a function of the components of q, in the case of a symmetric matrix pencil Aλ+C with A positive definite. It is known that R(q) has a stationary value when q is a characteristic vector of Aλ+C and that

(2)

where qi is a characteristic vector corresponding to the characteristic value λi

Given a complete Serre class τ this determines a torsion theory with T the class of torsion modules. It also determines the torsion free modules. For the classical torsion in the category of abelian groups the torsion free modules are flat and visa-versa. Which rings are characterized by this property? More precisely: Which rings admit a torsion theory for which the concepts of torsion free and flat are equivalent? We also dispose of the cases when R admits a toision theory for which torsion free is equivalent to injective and when projective is equivalent to torsion free.

Let (X, d) be a metric space and Ti(i=l, 2) be self mappings of X. The purpose of this paper is to investigate the fixed and common fixed points of Ti, when the pair Ti(i=l, 2) satisfies a condition of the following type:

(1)

The purpose of this paper is to define partially closed braids (§3) and to prove that every partially closed braid has a canonical form easily obtainable (§5). These objects are of interest because they can be used to represent knots tied in a string.

Braids have an obvious intuitive meaning to which we shall refer. Braids are also elements of the braid groups of E. Artin [1], defined for each integer n greater than one by the presentation

The Bell numbers Bn can be defined by Bn= where S(n, k) is t n e Stirling number of the second kind. In this note we employ a technique developed by Rota (which formalizes the umbral calculus) to derive a veriety of facts concerning the related numbers and polynomials .

Let X be a bounded region in the plane. Define

where f is an analytic function on X bounded in modulus by 1. We call d the Carathéodory metric.

In this note we give necessary and sufficient conditions to ensure that this metric be complete.

Borsuk has asked whether there exists for each compact metric absolute neighbourhood retract X an integer l (depending only on X) with the property that if X is homotopy equivalent to a cartesian product of more than l spaces than at least one of these spaces is contractible. The answer to this question is still not known. The following theorem has been proved by Ganea and Hilton [Theorem 1.3 of [1]].

In [3], Niven proved that for any positive integer k, the density of the set of positive integers n for which (n, (φ(n))≤k is zero (where φ is the Euler to tient function). In this paper, we prove a related result—namely if k and j are any positive integers, then the density of the set of positive integers n for which (n,σj(n))≤k is zero (where σj(n) is the sum of the jth powers of the positive divisors of n). We will borrow from Niven’s technique, but we must make some crucial modifications.

Let A be a complex Banach algebra without order. Following Kellogg [4] and Ching and Wong [2], a mapping T of A into itself is called a right (left) multiplier on A if T(ab)=(Ta)b(T(ab)=a(Tb)) for all a, b in A. T is said to be a multiplier on A if it is both a right and left multiplier on A. Let M(A)(RM(A), LM(A)) be the set of all (right, left) multipliers on A.

Let and let Gm be the group generated by A and the transpose of A. The problem of determining complex numbers m such that Gm is a free group had been studied by several authors [1, 2, 3]. In this note we characterize those rational values of m for which Gm is torsion free.

In [1,2] the sequence of polynomials

which we shall call Euler-Frobenius polynomials were considered and it was conjectured that these polynomials are irreducible in Q[x] for all odd values of n.

It has been shown by E. Granirer that for certain infinite amenable discrete groups G there exists a nested family of left almost convergent subsets of G on which every left invariant mean on m(G) attains as its range the entire [0,1] interval. This paper examines the range of left invariant means on L∞(G) for infinite locally compact abelian groups G and demonstrates the existence in every such group of a nested family of left almost convergent Borel subsets on which every left invariant mean on L∞ (G) attains as its range the interval [0,1],

Si S est un ensemble dénombrable sur lequel porte une chaîne de Markov, si pn(x, y) est la probabilité de transition de x à y au ne instant, on posera An(x) la totalité des y de S tels que pn(x, y)>0, ce sont les états accessibles à partir de x à l’instant n. Dans le cas de deux types de chaînes de Markov, nous recherchons des informations sur les états accessibles; ce sera premièrement les marches aléatoires sur Z et deuxièmement les processus de Galton-Watson sur ℕ. Nous recherchons en particulier les obstructions arithmétiques à ce qu’un état soit accessible.

Recently Howe [4] has considered the oscillation theory for the two-parameter eigenvalue problem

1a

1b

subjected to the boundary conditions

2a

2b

where for i = 1, 2, — ∞<ai<bi<∞, and qi are real-valued, continuous functions in [ai, bi], pi is positive in [ai, biz], and pi(ai)=pi(bi). Furthermore, it is also assumed that (A1B2—A2B1)≠0 for all values of x1 and x2 in their respective intervals.

In real Chebyshev approximation by generalized rational functions, constraining denominators to be positive guarantees that the set of best coefficients is convex [1, 181]. We show by means of an example that denominators must be constrained to be of constant argument for such a convexity result to hold in complex Chebyshev approximation.