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Let f(x) be a real function of the real variable x continuous at each point of the closed interval [a, b]. Then for every positive value of ε and for each point ξ of [a, b], it is possible to find an open interval N(ξ; δ) such that |f(x) – f(ξ)| < ε whenever the point x of [a,b] lies in N(ξ δ); indeed for each ξ there are an infinite number of such open intervals since, if N(ξ; δ1) is one such interval, so also is N(ξ; δ) for every δ < δ1 The infinite family {N(ξ δ):ξ ∈ [a, b]} of all these open intervals corresponding to all the points ξ of [a,b] is called an infinite open covering of [a, b]; every point of [a, b] belongs to at least one open interval of the family.
The Heine–Borel Theorem asserts that, from this infinite open covering of [a, b], we can select a finite number of open intervals of the family, which also covers [a, b]. Every point of [a, b] belongs to at least one of the open intervals of this finite open covering. From this follows the uniform continuity property, that, for every positive value of ∈, there exists a positive number Δ, depending on ∈, such that |f(x1) – f(x2)| < ε whenever the distance between the points x1 and x2 is less than Δ. We return to this in a more general context later.
This book, based on lectures given in the University of St Andrews, is intended to give honours students the background and training necessary before they start to study functional analysis.
There are many books on functional analysis; and some of them seem to go over the preliminaries to the subject far too quickly. The aim here is to provide a more leisurely approach to the theory of the topology of metric spaces, a subject which is not only the basis of functional analysis but also unifies many branches of classical analysis. The applications of the theory in Chapter 8 to problems in classical algebra and analysis show how much can be done without ever defining a normed vector space, a Banach space or a Hilbert space.
The reader is not expected to know much more classical analysis than is contained in Hardy's Pure Mathematics or Burkill's First Course in Mathematical Analysis. A knowledge of the elements of the theory of uniform convergence is assumed. Analytic functions and Lebesgue integrals are mentioned occasionally; their introduction provides more advanced applications of the theory of metric spaces, but adds nothing to the theory.
I am most grateful to Professor Arthur Erdélyi and to the Editors of the series of Cambridge Mathematical Tracts for their kindly criticisms and suggestions.
I wish to thank Mr Frank Gerrish and Professor Edwin Hewitt for many corrections, which have proved invaluable to me in the preparation of the second impression of this book.
This chapter is concerned with the extension of the idea of continuity to a function defined on an abstract set and taking values in an abstract set, possibly the same set. We recall the definition of a function or mapping given in Chapter 1.
Let E1 and E2 be two non-empty sets. By a mapping f of E1into E2 we mean a relation which associates with each element a of E1 a single well-defined element of E2 denoted by f(a) and called the image of a under the mapping f. The mapping f of E1 into E2 is denoted by f: E1 → E2. The set E1 is called the domain of the mapping; the set {f(a): α ∈ E1 of all points of E2 which are images of points of E2 is called the range of f. The range may be a proper subset of E2; it may even be a single point, in which case the mapping is called a constant mapping. A function is, by definition, one-valued.
Another way of picturing a mapping is a generalization of the graph of elementary calculus. Consider the Cartesian product E1 × E2 which is the set of all ordered pairs (x,y) where x ∈ E1, y ∈ E2 A mapping or function f: E1 → E2 is a particular sort of subset of E1 × E2; a subset with the property that, amongst the ordered pairs (x, y) which form the function, each point a of E1 occurs once and once only.
Recently a power series representation of Hypergeometric functions with matrix argument has been established. This representation involves a special type of spherical function from the theory of semi-simple Lie groups, called the zonal polynomials. A general theory of these polynomials is well established; however an explicit representation of them is lacking. This paper considers two integrals which are related to this explicit representation. The final paragraph considers a third integral which gives an application of a result from a previous paper of the author.
Unsuccessful efforts to synthesize benzo[a]biphenylene and dibenzo-biphenylenes by the dehydrohalogenation of suitable intermediates are described. 2-o-Chlorophenyl-2-phenylpropionitrile with potassamide in liquid ammonia failed to give 8-cyano-7-phenylbicyclo[4,2,o]octa-I,3,5-triene, while diethyl 2-bromobenzylphenylmalonate with sodium in dry ethanol yielded I-phenylisochroman-3-one after hydrolysis. Bromination of 3,3′,4,4′-tetrahydro-2,2′-binaphthyl was accompanied by spontaneous dehydrobromination to yield 2,2′-binaphthyl, and interaction of phenyl-o-chlorophenylbromomethane with phenyllithium followed by chloracetic acid gave 1,2-di-o-chlorophenylethane.
It is the custom of our Society that the President of the day should at some period in his term of office address the Fellows. The manner in which he interprets this charge will, of course, vary according to individual preference, but for obvious reasons, he usually elects to give his personal interpretation of that area of science in which he is himself most deeply concerned.
Our Society was founded in the days before science was split into highly specialized sections and long before the advent of the specialist societies restricted to one scientific discipline, such as the Chemical Society, the Biochemical Society or the Society for Experimental Biology. This, in the opinion of many of our Fellows, is its main strength, since, as a general Society concerned with all aspects of science, it can exert an integrative function; in fact, it serves many of the purposes of the Academies which are so well known in other parts of Europe, as is made clear in the Letters Patent granting our Armorial Bearings.
By means of a generalized ring of quotients multiplicative ideal theory is studied in an arbitrary (associative) ring. A suitable generalization of the concept of maximal order is given and factorization theorems are obtained for the nonsingular (two sided) ideals, which generalize the theorems of Artin and E. Noether.
This paper studies two particular cases of the general 2-parameter eigenvalue problem namely
where A, B, B1, B2, C, C1, C2 are self-adjoint operators in Hilbert space, all except A being bounded. The disposable parameters λ and μ have to be determined so that the equations have non-trivial solutions x, y.
On the assumption that the solution is known for ∊ = o, solutions are constructed in the form of series for λ, μ, x, y as power series in ∊ with finite radius of convergence.
The Langevin equation for the harmonic oscillator is solved by a different method from that normally used. The approximate solution for the case of the slightly anharmonic oscillator is then obtained by an iterative procedure and the results are illustrated by a numerical example based on a simple model of a crystalline solid.
Let A be a subset of a compact metric space Ω, and suppose that A has non-σ-finite h-measure, where h is some Hausdorff function. The following problem was suggested to me by Professor C. A. Rogers:
If A is analytic, is it possible to construct 2ℵodisjoint closed subsets of A which also have non-σ-finite h-measure?
At this level of generality the problem, like others which involve selection of subsets, appears to offer some difficulty. Here we prove two results which were motivated by it.
Truesdell and Noll [1; sections 22, 27, 34] have discussed the concepts of material uniformity and homogeneity in continuum mechanics. A body is said to be materially uniform if, roughly speaking, all the particles composing the body are of the same material and homogeneous if there exists a global reference configuration which can be taken as a natural state for the whole body. To make the ideas precise for elastic materials, consider a small neighbourhood of each particle X and suppose that a reference configuration κ is chosen for each . Then during the motion, the deformation gradients may be calculated at each point X relative to the local reference configurations k. The stress at X is a function of these deformation gradients and if the stress relation does not depend explicitly on X the body is said to be materially uniform. If each local reference configuration κ can be taken as the configuration of its associated set of particles in some global reference configuration for the whole body, the body is said to be homogeneous. In general, however, the configurations κ need not fit together to form a global reference configuration. The body is then said to contain a distribution of dislocations.