The graph-theoretic analogue of Tietze's characterization of a convex set and its generalization

1972 ◽  
Vol 72 (1) ◽  
pp. 7-9
Author(s):  
M. D. Guay
Keyword(s):  
Linear Space ◽  
Closed Subset ◽  
Convex Sets ◽  
Convex Set ◽  
Topological Linear Space ◽  
Connected Subset ◽  
Graph Theoretic ◽  
Topological Linear ◽  
Locally Convex

Introduction. One of the most satisfying theorems in the theory of convex sets states that a closed connected subset of a topological linear space which is locally convex is convex. This was first established in En by Tietze and was later extended by other authors (see (3)) to a topological linear space. A generalization of Tietze's theorem which appears in (2) shows if S is a closed subset of a topological linear space such that the set Q of points of local non-convexity of S is of cardinality n < ∞ and S ~ Q is connected, then S is the union of n + 1 or fewer convex sets. (The case n = 0 is Tietze's theorem.)

TOPOLOGICAL TOMOGRAPHY IN CONVEXITY

2002 ◽  
Vol 34 (3) ◽  
pp. 353-358
Author(s):  
L. MONTEJANO ◽  
E. SHCHEPIN
Keyword(s):  
Linear Space ◽  
Convex Sets ◽  
Compact Convex ◽  
Weakly Closed ◽  
Locally Convex

The main theorem of this paper generalizes a classic Aumann's characterization of compact convex sets, via the acyclicity of their hypersections, to arbitrary weakly closed subsets of a locally convex linear space.

A Tauberian theorem for statistical convergence

1989 ◽  
Vol 106 (2) ◽  
pp. 277-280 ◽  
Author(s):  
I. J. Maddox
Keyword(s):  
Linear Space ◽  
Tauberian Theorem ◽  
Statistical Convergence ◽  
Slow Oscillation ◽  
Topological Linear Space ◽  
Tauberian Condition ◽  
Topological Linear ◽  
Locally Convex

The notion of statistical convergence of a sequence (xk) in a locally convex Hausdorff topological linear space X was introduced recently by Maddox[5], where it was shown that the slow oscillation of (sk) was a Tauberian condition for the statistical convergence of (sk).

scholarly journals Multipliers and operators on the tempered ultradistribution spaces of Roumieu type for the distributional Hankel-type transformation spaces

2006 ◽  
Vol 2006 ◽  
pp. 1-7
Author(s):  
P. K. Banerji ◽  
S. K. Al-Omari
Keyword(s):  
Linear Space ◽  
Topological Linear Space ◽  
Type Transformation ◽  
Topological Linear ◽  
Locally Convex

The tempered ultradistribution space of Roumieu type for the spaceHμ,νis defined, which is a subspace of the Hausdörff locally convex topological linear space. Further, results are obtained for the multipliers and operators on the tempered ultradistribution spaces for the distributional Hankel-type transformation spaces.

On Unions of Two Convex Sets

1966 ◽  
Vol 18 ◽  
pp. 883-886 ◽  
Author(s):  
Richard L. McKinney
Keyword(s):  
Linear Space ◽  
Convex Sets ◽  
Convexity Property ◽  
Topological Linear Space ◽  
Closed Sets ◽  
Connected Set ◽  
Point Convexity ◽  
Topological Linear ◽  
Convex Subsets ◽  
Compact Subsets

Valentine (3) introduced the three-point convexity property P3 : a set S in En satisfies P3 if for each triple of points x, y, z in S at least one of the closed segments xy, yz, xz is in S. He proved, (3 or 1) that in the plane a closed connected set satisfying P3 is the union of some three convex subsets. The problem of characterizing those sets that are the union of two convex subsets was suggested. Stamey and Marr (2) have provided an answer for compact subsets of the plane. We present here a generalization of property P3 which characterizes closed sets in an arbitrary topological linear space which are the union of two convex subsets.

scholarly journals Tilings of Normed Spaces

2017 ◽  
Vol 69 (02) ◽  
pp. 321-337 ◽  
Author(s):  
Carlo Alberto De Bernardi ◽  
Libor Veselý
Keyword(s):  
Pairwise Disjoint ◽  
Convex Sets ◽  
The Other ◽  
Locally Convex Spaces ◽  
List Type ◽  
Topological Linear Space ◽  
Normed Spaces ◽  
Infinite Dimensional ◽  
Topological Linear ◽  
Locally Convex

Abstract By a tiling of a topological linear space X, we mean a covering of X by at least two closed convex sets, called tiles, whose nonempty interiors are pairwise disjoint. Study of tilings of infinite dimensional spaceswas initiated in the 1980's with pioneer papers by V. Klee. We prove some general properties of tilings of locally convex spaces, and then apply these results to study the existence of tilings of normed and Banach spaces by tiles possessing certain smoothness or rotundity properties. For a Banach space X, our main results are the following. (i) X admits no tiling by Fréchet smooth bounded tiles. (ii) If X is locally uniformly rotund (LUR), it does not admit any tiling by balls. (iii) On the other hand, some spaces, г uncountable, do admit a tiling by pairwise disjoint LUR bounded tiles.

On the convex kernel of a compact set

1967 ◽  
Vol 63 (2) ◽  
pp. 311-313 ◽  
Author(s):  
D. G. Larman
Keyword(s):  
Linear Space ◽  
Compact Subset ◽  
Line Segment ◽  
Linear Dimension ◽  
Single Point ◽  
Compact Set ◽  
Topological Linear Space ◽  
Topological Linear

Suppose that E is a compact subset of a topological linear space ℒ. Then the convex kernel K, of E, is such that a point k belongs to K if every point of E can be seen, via E, from k. Valentine (l) has asked for conditions on E which ensure that the convex kernel K, of E, consists of exactly one point, and in this note we give such a condition. If A, B, C are three subsets of E, we use (A, B, C) to denote the set of those points of E, which can be seen, via E, from a triad of points a, b, c, with a ∈ A, b ∈ B, c ∈ C. We shall say that E has the property if, whenever A is a line segment and B, C are points of E which are not collinear with any point of A, the set (A, B, C) has linear dimension of at most one, and degenerates to a single point whenever A is a point.

scholarly journals Auerbach Bases and Minimal Volume Sufficient Enlargements

2011 ◽  
Vol 54 (4) ◽  
pp. 726-738
Author(s):  
M. I. Ostrovskii
Keyword(s):  
Linear Space ◽  
Isometric Embedding ◽  
Normed Linear Space ◽  
Convex Set ◽  
Linear Projection ◽  
Minimal Volume ◽  
Finite Dimensional ◽  
Dimensional Normed Space ◽  
Closed Convex Set

AbstractLet BY denote the unit ball of a normed linear space Y. A symmetric, bounded, closed, convex set A in a finite dimensional normed linear space X is called a sufficient enlargement for X if, for an arbitrary isometric embedding of X into a Banach space Y, there exists a linear projection P: Y → X such that P(BY ) ⊂ A. Each finite dimensional normed space has a minimal-volume sufficient enlargement that is a parallelepiped; some spaces have “exotic” minimal-volume sufficient enlargements. The main result of the paper is a characterization of spaces having “exotic” minimal-volume sufficient enlargements in terms of Auerbach bases.

scholarly journals Matrix transformations and convex spaces

1988 ◽  
Vol 11 (3) ◽  
pp. 585-588
Author(s):  
I. J. Maddox
Keyword(s):  
Linear Space ◽  
Matrix Transformations ◽  
Topological Linear Space ◽  
Sequential Completeness ◽  
Metrizable Spaces ◽  
Topological Linear ◽  
Convex Spaces

In a Hausdorff topological linear space we examine relations betweenr-convexity and a condition on matrix transformations between null sequences. In particular, for metrizable spaces the condition impliesr-convexity. For locally bounded spaces the condition implies sequential completeness.

C(X) As A Dual Space

1972 ◽  
Vol 24 (3) ◽  
pp. 485-491 ◽  
Author(s):  
E. G. Manes
Keyword(s):  
Banach Space ◽  
Linear Space ◽  
Dual Space ◽  
Minkowski Functional ◽  
Topological Linear Space ◽  
Open Set ◽  
Topological Linear

It is known [1] that for compact Hausdorff X, C(X) is the dual of a Banach space if and only if X is hyperstonian, that is the closure of an open set in X is again open and the carriers of normal measures in C(X)* have dense union in X. With the desiratum of proving that C(X) is always the dual of some sort of space we broaden the concept of Banach space as follows. A Banach space may be comfortably regarded as a pair (E, B) where E is a topological linear space and B is a subset of E ; the requisite property is that the Minkowski functional of B be a complete norm whose topology coincides with that of E.

A geometric characterization concerning compact, convex sets

1991 ◽  
Vol 109 (2) ◽  
pp. 351-361 ◽  
Author(s):  
Christopher J. Mulvey ◽  
Joan Wick Pelletier
Keyword(s):  
Normed Space ◽  
Convex Sets ◽  
Convex Set ◽  
Compact Convex ◽  
Necessary And Sufficient Condition ◽  
Categorical Logic ◽  
Compact Convex Set ◽  
Necessary And Sufficient ◽  
Formal Statement

In this paper, we are concerned with establishing a characterization of any compact, convex set K in a normed space A in an arbitrary topos with natural number object. The characterization is geometric, not in the sense of categorical logic, but in the intuitive one, of describing any compact, convex set K in terms of simpler sets in the normed space A. It is a characterization of the compact, convex set in the sense that it provides a necessary and sufficient condition for an element of the normed space to lie within it. Having said this, we should immediately qualify our statement by stressing that this is the intuitive content of what is proved; the formal statement of the characterization is required to be in terms appropriate to the constructive context of the techniques used.

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