Weak-open images of locally separable metric spaces

2011 ◽  
Vol 48 (2) ◽  
pp. 145-159
Author(s):  
Zhaowen Li ◽  
Xun Ge ◽  
Qingguo Li
Keyword(s):  
Metric Space ◽  
Metric Spaces ◽  
Weak Base ◽  
Cosmic Space ◽  
Locally Separable Metric Spaces ◽  
Separable Metric Space

In this paper, we prove that a space X is a weak-open compact image of a locally separable metric space if and only if X has a uniform cosmic-weak-base if and only if X is a weak-open compact image of a metric space and a locally cosmic space, and give some internal characterizations of weak-open s-images of locally separable metric spaces.

scholarly journals Further results on images of metric spaces

2015 ◽  
Vol 98 (112) ◽  
pp. 179-191
Author(s):  
Van Dung
Keyword(s):  
Metric Space ◽  
Metric Spaces ◽  
Sufficient Conditions ◽  
Necessary And Sufficient Conditions ◽  
Weakly Continuous ◽  
Locally Separable Metric Spaces ◽  
Necessary And Sufficient ◽  
Separable Metric Space

We introduce the notion of an ls-?-Ponomarev-system to give necessary and sufficient conditions for f:(M,M0) ? X to be a strong wc-mapping (wc-mapping, wk-mapping) where M is a locally separable metric space. Then, we systematically get characterizations of weakly continuous strong wc-images (wc-images, wk-images) of locally separable metric spaces by means of certain networks. Also, we give counterexamples to sharpen some results on images of locally separable metric spaces in the literature.

scholarly journals A Universal Separable Diversity

2017 ◽  
Vol 5 (1) ◽  
pp. 138-151 ◽  
Author(s):  
David Bryant ◽  
André Nies ◽  
Paul Tupper
Keyword(s):  
Metric Space ◽  
Metric Spaces ◽  
Complete Metric Space ◽  
Urysohn Space ◽  
Fundamental Properties ◽  
Finite Set ◽  
Whole Space ◽  
Set Of Points ◽  
Separable Metric Space

AbstractThe Urysohn space is a separable complete metric space with two fundamental properties: (a) universality: every separable metric space can be isometrically embedded in it; (b) ultrahomogeneity: every finite isometry between two finite subspaces can be extended to an auto-isometry of the whole space. The Urysohn space is uniquely determined up to isometry within separable metric spaces by these two properties. We introduce an analogue of the Urysohn space for diversities, a recently developed variant of the concept of a metric space. In a diversity any finite set of points is assigned a non-negative value, extending the notion of a metric which only applies to unordered pairs of points.We construct the unique separable complete diversity that it is ultrahomogeneous and universal with respect to separable diversities.

scholarly journals Paths in hyperspaces

2003 ◽  
Vol 4 (2) ◽  
pp. 377 ◽  
Author(s):  
Camillo Constantini ◽  
Wieslaw Kubís
Keyword(s):  
Metric Space ◽  
Metric Spaces ◽  
Hausdorff Metric ◽  
Absolute Retract ◽  
Almost Convex ◽  
Convex Metric Spaces ◽  
Metric Topology ◽  
Hausdorff Metric Topology ◽  
Bounded Sets ◽  
Separable Metric Space

<p>We prove that the hyperspace of closed bounded sets with the Hausdor_ topology, over an almost convex metric space, is an absolute retract. Dense subspaces of normed linear spaces are examples of, not necessarily connected, almost convex metric spaces. We give some necessary conditions for the path-wise connectedness of the Hausdorff metric topology on closed bounded sets. Finally, we describe properties of a separable metric space, under which its hyperspace with the Wijsman topology is path-wise connected.</p>

Distance Sets of Urysohn Metric Spaces

2013 ◽  
Vol 65 (1) ◽  
pp. 222-240 ◽  
Author(s):  
N.W. Sauer
Keyword(s):  
Metric Space ◽  
Metric Spaces ◽  
Finite Metric Space ◽  
Distance Set ◽  
Distance Sets ◽  
Separable Metric Space

Abstract.A metric space M = (M; d) is homogeneous if for every isometry f of a finite subspace of M to a subspace of M there exists an isometry of M onto M extending f . The space M is universal if it isometrically embeds every finite metric space F with dist(F) ⊆ dist(M) (with dist(M) being the set of distances between points in M).A metric space U is a Urysohn metric space if it is homogeneous, universal, separable, and complete. (We deduce as a corollary that a Urysohn metric space U isometrically embeds every separable metric space M with dist(M) ⊆ dist(U).)The main results are: (1) A characterization of the sets dist(U) for Urysohn metric spaces U. (2) If R is the distance set of a Urysohn metric space and M and N are two metric spaces, of any cardinality with distances in R, then they amalgamate disjointly to a metric space with distances in R. (3) The completion of every homogeneous, universal, separable metric space M is homogeneous.

Sequentially continuous linear mappings in constructive analysis

1998 ◽  
Vol 63 (2) ◽  
pp. 579-583 ◽  
Author(s):  
Douglas Bridges ◽  
Ray Mines
Keyword(s):  
Metric Space ◽  
Metric Spaces ◽  
Continuous Mapping ◽  
Constructive Mathematics ◽  
Closed Graph Theorem ◽  
Inverse Mapping ◽  
Inverse Mapping Theorem ◽  
Continuous Mappings ◽  
Sequential Continuity ◽  
Separable Metric Space

A mapping u: X → Y between metric spaces is sequentially continuous if for each sequence (xn) converging to x ∈ X, (u(xn)) converges to u(x). It is well known in classical mathematics that a sequentially continuous mapping between metric spaces is continuous; but, as all proofs of this result involve the law of excluded middle, there appears to be a constructive distinction between sequential continuity and continuity. Although this distinction is worth exploring in its own right, there is another reason why sequential continuity is interesting to the constructive mathematician: Ishihara [8] has a version of Banach's inverse mapping theorem in functional analysis that involves the sequential continuity, rather than continuity, of the linear mappings; if this result could be upgraded by deleting the word “sequential”, then we could prove constructively the standard versions of the inverse mapping theorem and the closed graph theorem.Troelstra [9] showed that in Brouwer's intuitionistic mathematics (INT) a sequentially continuous mapping on a separable metric space is continuous. On the other hand, Ishihara [6, 7] proved constructively that the continuity of sequentially continuous mappings on a separable metric space is equivalent to a certain boundedness principle for subsets of ℕ; in the same paper, he showed that the latter principle holds within the recursive constructive mathematics (RUSS) of the Markov School. Since it is not known whether that principle holds within Bishop's constructive mathematics (BISH), of which INT and RUSS are models and which can be regarded as the constructive core of mathematics, the exploration of sequential continuity within BISH holds some interest.

scholarly journals Isometry groups of separable metric spaces

2009 ◽  
Vol 146 (1) ◽  
pp. 67-81 ◽  
Author(s):  
MACIEJ MALICKI ◽  
SŁAWOMIR SOLECKI
Keyword(s):  
Metric Space ◽  
Isometry Group ◽  
Metric Spaces ◽  
Structure Theorem ◽  
Ultrametric Space ◽  
Isometry Groups ◽  
Locally Compact ◽  
Natural Action ◽  
Polish Group ◽  
Separable Metric Space

AbstractWe show that every locally compact Polish group is isomorphic to the isometry group of a proper separable metric space. This answers a question of Gao and Kechris. We also analyze the natural action of the isometry group of a separable ultrametric space on the space. This leads us to a structure theorem representing an arbitrary separable ultrametric space as a bundle with an ultrametric base and with ultrahomogeneous fibers which are invariant under the action of the isometry group.

scholarly journals Peano compactifications and propertySmetric spaces

1980 ◽  
Vol 3 (4) ◽  
pp. 695-700
Author(s):  
R. F. Dickman
Keyword(s):  
Metric Space ◽  
Metric Spaces ◽  
Metrizable Space ◽  
Connected Sets ◽  
Metrizable Spaces ◽  
Necessary And Sufficient ◽  
Separable Metric Space

Let(X,d)denote a locally connected, connected separable metric space. We say theXisS-metrizable provided there is a topologically equivalent metricρonXsuch that(X,ρ)has PropertyS, i.e. for anyϵ>0,Xis the union of finitely many connected sets ofρ-diameter less thanϵ. It is well-known thatS-metrizable spaces are locally connected and that ifρis a PropertySmetric forX, then the usual metric completion(X˜,ρ˜)of(X,ρ)is a compact, locally connected, connected metric space, i.e.(X˜,ρ˜)is a Peano compactification of(X,ρ). There are easily constructed examples of locally connected connected metric spaces which fail to beS-metrizable, however the author does not know of a non-S-metrizable space(X,d)which has a Peano compactification. In this paper we conjecture that: If(P,ρ)a Peano compactification of(X,ρ|X),Xmust beS-metrizable. Several (new) necessary and sufficient for a space to beS-metrizable are given, together with an example of non-S-metrizable space which fails to have a Peano compactification.

n-ANR's for Certain Normal Spaces

1967 ◽  
Vol 19 ◽  
pp. 629-635 ◽  
Author(s):  
Vincent J. Mancuso
Keyword(s):  
Metric Space ◽  
Metric Spaces ◽  
Separable Metric Space

For various classes Q of metric spaces, there are several well-known results characterizing the local n-connectivity of a metric space in terms of n-ANR(Q)'s. Specifically, we have in mind the results of Kuratowski (13, p. 265) and Kodama (10, p. 79). The main purpose of this paper will be to obtain similar results along these lines for non-metric classes Q. In the last part of the paper we specify Q to be the class of totally normal spaces and characterize the local n-connectivity of an n-dimensional separable metric space in terms of ANR(Q)'s.

REVERSE MATHEMATICS OF MF SPACES

2006 ◽  
Vol 06 (02) ◽  
pp. 203-232 ◽  
Author(s):  
CARL MUMMERT
Keyword(s):  
Metric Space ◽  
Closed Subset ◽  
Metric Spaces ◽  
Reverse Mathematics ◽  
General Topology ◽  
Second Order Arithmetic ◽  
Perfect Set ◽  
Order Arithmetic ◽  
Complete Separable Metric Space ◽  
Separable Metric Space

This paper gives a formalization of general topology in second-order arithmetic using countably based MF spaces. This formalization is used to study the reverse mathematics of general topology. For each poset P we let MF (P) denote the set of maximal filters on P endowed with the topology generated by {Np | p ∈ P}, where Np = {F ∈ MF (P) | p ∈ F}. We define a countably based MF space to be a space of the form MF (P) for some countable poset P. The class of countably based MF spaces includes all complete separable metric spaces as well as many nonmetrizable spaces. The following reverse mathematics results are obtained. The proposition that every nonempty Gδ subset of a countably based MF space is homeomorphic to a countably based MF space is equivalent to [Formula: see text] over ACA0. The proposition that every uncountable closed subset of a countably based MF space contains a perfect set is equivalent over [Formula: see text] to the proposition that [Formula: see text] is countable for all A ⊆ ℕ. The proposition that every regular countably based MF space is homeomorphic to a complete separable metric space is equivalent to [Formula: see text] over [Formula: see text].

On Asymmetric Distances

2013 ◽  
Vol 1 ◽  
pp. 200-231 ◽  
Author(s):  
Andrea C.G. Mennucci
Keyword(s):  
Total Variation ◽  
Calculus Of Variations ◽  
Distance Function ◽  
Metric Space ◽  
Metric Spaces ◽  
Geodesic Segment ◽  
Intrinsic Metric ◽  
Typical Application ◽  
Variation Formula

Abstract In this paper we discuss asymmetric length structures and asymmetric metric spaces. A length structure induces a (semi)distance function; by using the total variation formula, a (semi)distance function induces a length. In the first part we identify a topology in the set of paths that best describes when the above operations are idempotent. As a typical application, we consider the length of paths defined by a Finslerian functional in Calculus of Variations. In the second part we generalize the setting of General metric spaces of Busemann, and discuss the newly found aspects of the theory: we identify three interesting classes of paths, and compare them; we note that a geodesic segment (as defined by Busemann) is not necessarily continuous in our setting; hence we present three different notions of intrinsic metric space.

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