### Browsing by Author "Webb, John H"

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- ItemOpen AccessAscent, descent, nullity and defect of linear operators(1974) Nichol, John Robert; Webb, John H; Smart, D RThis thesis is intended to be a survey of nullity and defect of linear operators on the one hand, and ascent and descent on the other, and the relationships between these concepts. These quantities are of considerable use in the discussion of linear operators, e.g. compact operators.
- ItemOpen AccessCountable inductive limits(1972) Martens, Eric; Webb, John HInductive systems and inductive limits have by now become fairly well established in the general theory of topological vector spaces. It is a branch of Functional Analysis which is receiving a reasonable amount of attention by modern mathematicians. It is of course a very interesting subject of its own accord, but is also useful in solving problems and proving theorems which one does not suspect are intimately related to it. As an example we can consider the proof of the non-existence of a countably infinite dimensional metrisable barrelled space.
- ItemOpen AccessGeneralized DF spaces(1984) Robertson, Neill Raymond Charles; Webb, John HA DF space is a topological vector space sharing certain essential properties with the strong duals of Frechet spaces. The class of DF spaces includes not only all such duals, but also every· normed space and many other spaces besides. The definition of a DF space is due to Grothendieck, who derived almost all the important results concerning such spaces. The "generalized DF spaces" in the title of this thesis are locally convex topological vector spaces whose topologies are determined by their restrictions to an absorbent sequence of bounded sets. In the case when this sequence is a fundamental sequence of bounded sets, we obtain the gDF spaces. Many. of the properties of DF spaces are shared by all gDF spaces.
- ItemOpen AccessSeparability and metrisability in locally convex spaces(1991) Robertson, Neill Raymond Charles; Webb, John HThis thesis is devoted to a study of the relationship between separability and metrisability in the context of locally convex spaces. The duality between sep- arability and weak*-metrisability does not carry over to non-metrisable locally convex spaces; the best that can be said in this case is that the equicontinuous subsets in the dual of a separable locally convex space are weak*-metrisable. To get around this difficulty, we often prefer to use the idea of separability by seminorm: a locally convex space E is separable by seminorm if and only if the equicontinuous subsets of its dual are weak*-metrisable. On any locally convex space E there is a finest topology Tχ which is coarser than the given topology and which makes E separable by seminorm. A question that arises is under what conditions a space E is Tχ-complete. In trying to answer this question, we are led to an intriguing binary relation which G.A. Edgar originally defined on the class of Banach spaces. In the first two Chapters of this thesis, we show that many of the results in Edgar's paper can be expressed in terms of the completeness of a space with respect to various topologies.
- ItemOpen AccessStability of barrelled topologies(1983) Burton, Michael Howard; Webb, John HIn the theory of locally convex topological vector spaces, barrelled topologies have been found to be stable under the formation of products, sums and quotients. We shall in this thesis investigate the stability of barrelled topologies with respect to two further mathematical constructions. Firstly, we examine the situation with regard to the formation of finite-codimensional and countable-codimensional subspaces. (Of course, barrelled topologies are not stable under the formation of arbitrary subspaces.) Secondly, we present what is known about the stability of barrelled topologies with respect to enlargements of the dual space - a concept which is defined in the sequel. This aspect of the stability question was tackled in a recent paper by Robertson and Yeomans and was pursued in two subsequent papers by Tweddle and Yeomans and by Robertson, Tweddle and Yeomans. In the next two chapters, we turn our attention to quasibarrelled topologies and we pursue a parallel investigation to that of the first two chapters. Finally we conduct a similar investigation on σ-barrelled and σ-quasibarrelled spaces. The results 5.2, 5.3, 5.4, 5.5, 5.6, 6.2, 6.3, 6.4 and 6.5 concerning these spaces are original.
- ItemOpen AccessThe theory and some applications of Pták's method of non-discrete mathematical induction(1977) Marsh, Terence Anthony; Webb, John HThe aim of this thesis is three-fold: (1) to develop the theory of small functions; (2) to synthesize Pták's work presented in his papers [10], [11], ..., [16] into a coherent body of knowledge; (3) to elaborate on Pták's work (i) by providing small function generalizations of Banach's Fixed Point Theorem and Edelstein's Extended Contraction Principle; (ii) by connecting the Induction Theorem to Baire's Category Theorem and Cantor's Intersection Theorem. Throughout the exposition the editorial "we" is to be understood in the sense of Halmos [ 18]; "we" means "the author and the reader".