DOCSLIB.ORG

TOPOLOGICAL PROPERTIES of NON-ARCHIMEDEAN APPROACH SPACES 1. Introduction

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
TOPOLOGICAL PROPERTIES of NON-ARCHIMEDEAN APPROACH SPACES 1. Introduction Theory and Applications of Categories, Vol. 32, No. 41, 2017, pp. 1454{1484. TOPOLOGICAL PROPERTIES OF NON-ARCHIMEDEAN APPROACH SPACES EVA COLEBUNDERS AND KAREN VAN OPDENBOSCH Abstract. In this paper we give an isomorphic description of the category of non- Archimedian approach spaces as a category of lax algebras for the ultrafilter monad and an appropriate quantale. Non-Archimedean approach spaces are characterised as those approach spaces having a tower consisting of topologies. We study topological properties p; for p compactness and Hausdorff separation along with low-separation properties, regularity, normality and extremal disconnectedness and link these properties to the condition that all or some of the level topologies in the tower have p. A compactification technique is developed based on Shanin's method. 1. Introduction In monoidal topology [Hofmann, Seal, Tholen (eds.), 2014] starting from the quantale op P+ = [0; 1] ; +; 0 where the natural order ≤ of the extended real halfline [0; 1] is reversed so that 0 = > and 1 = ?, based on Lawvere's description of quasi-metric spaces as categories enriched over the extended real line [Lawvere 1973], one obtains an isomorphism between the category qMet of extended quasi-metric spaces with non- expansive maps and P+ -Cat, the category of P+ -spaces (X; a), where X is a set and a : X−!7 X is a transitive and reflexive P+ -relation, meaning it is a map a : X × X ! P+ satisfying a(x; y) ≤ a(x; z) + a(z; y) and a(x; x) = 0 for all x; y; z in X; with morphisms 0 0 0 f :(X; a) ! (Y; b) of P+ -Cat, maps satisfying b(f(x); f(x )) ≤ a(x; x ) for all x; x in X: Our interest goes to the larger category App of approach spaces and contractions, which contains qMet as coreflectively embedded full subcategory and which is better behaved than qMet with respect to products of underlying topologies. A comprehensive source on approach spaces and their vast field of applications is [Lowen, 2015] in which several equivalent descriptions of approach spaces are formulated in terms of (among others) distances, limit operators, towers and gauges. A first lax-algebraic description of approach spaces was established by Clementino and Hofmann in [Clementino, Hofmann, 2003]. The construction involves the ultrafilter monad = (β; m; e), the quantale P+ and an extension of the ultrafilter monad to P+ -relations. The so constructed category ( ; P+ )-Cat and its isomorphic description App became an important example in the development of monoidal topology [Hofmann, Seal, Tholen (eds.), 2014]. More details on the construction will be Received by the editors 2017-07-17 and, in final form, 2017-11-01. Transmitted by Walter Tholen. Published on 2017-11-13. 2010 Mathematics Subject Classification: 18C15, 18C20, 54A05, 54B30, 54E99. Key words and phrases: Lax algebra, quantale, non-Archimedean approach space, quasi-ultrametric space, initially dense object, topological properties in ( ; P_ )-Cat, compactification. c Eva Colebunders and Karen Van Opdenbosch, 2017. Permission to copy for private use granted. 1454 TOPOLOGICAL PROPERTIES OF NON-ARCHIMEDEAN APPROACH SPACES 1455 recalled in section 2. In this paper we consider the non-Archimedian counterparts of the previous well known constructions. These are obtained by switching the quantale to P_ . As before we consider the extended real halfline [0; 1] as a complete lattice with respect to the natural order ≤ and we reverse its order, so that 0 = > is the top and 1 = ? is the bottom element. Since [0; 1]op is a chain, it is a frame, and we may consider it a quantale with its meet operation which, according to our conventions on the reversed order, is the supremum with respect to the natural order of [0; 1] and as in approach theory this operation will be denoted by _ (note that here we deviate from the notation in [Hofmann, Seal, Tholen (eds.), 2014]). As stated in exercise III.2.B of [Hofmann, Seal, Tholen (eds.), 2014] the u category P_ -Cat is isomorphic to the category qMet of extended quasi-ultrametric spaces (X; d) with non-expansive maps, where an extended quasi-metric is called an extended quasi-ultrametric if it satisfies the strong triangular inequality d(x; z) ≤ d(x; y) _ d(y; z); for all x; y; z 2 X. In section 2, using the ultrafilter monad = (β; m; e), with P_ as quantale and an extension of the ultrafilter monad to P_ -relations we show that the category of associated lax algebras ( ; P_ )-Cat is isomorphic to the reflectively embedded full subcategory NA-App of App; the objects of which are called non-Archimedean approach spaces. In section 3 we give equivalent descriptions of non-Archimedean approach spaces in terms of distances, limit operators, towers and gauges. The characterization in terms of towers can be easily expressed: an approach space is non-Archimedean if and only if its tower (T")"2R+ consists of topologies. We show that NA-App can be generated as the concretely reflective hull by one particular extended quasi-ultrametric. Following the general philosophy to consider lax algebras as spaces, it is our main purpose in this paper to study topological properties p like compactness and Hausdorff separation, along with low-separation properties, regularity, normality and extremal dis- connectedness for non-Archimedean approach spaces. In section 6 we introduce these T properties ( ; P_ )-p as an application to ( ; P_ )-Cat of the corresponding ( ; V)-properties for arbitrary (T; V)-Cat as developed in V.1 and V.2 of [Hofmann, Seal, Tholen (eds.), 2014]. For each of the properties p we characterise ( ; P_ )-p in the context of NA-App. On the other hand we make use of the well known meaning of these properties in the setting of Top and for a non-Archimedean approach space X with tower of topologies + (T")"2R we compare the property ( ; P_ )-p to the properties X has p at level 0, meaning the topological space (X; T0) has p in Top;X almost strongly has p, meaning (X; T") has R+ p in Top for every " 2 0 and X strongly has p, meaning (X; T") has p in Top for every " 2 R+: For p the Hausdorff property, low separation properties or regularity the condi- tions strongly p, almost strongly p and ( ; P_ )-p are all equivalent and different from p at level 0: For p compactness strongly p is equivalent to p at level 0, and almost strongly p is equivalent to ( ; P_ )-p. For p normality or extremal disconnectedness strongly p implies almost strongly p which implies ( ; P_ )-p. Moreover strongly p implies p at level 0. We give counterexamples showing that there are no other valid implications. In the last sections of the paper we develop a compactification technique and prove 1456 EVA COLEBUNDERS AND KAREN VAN OPDENBOSCH that every non-Archimedean approach space X given by its tower of topologies (T")"2R+ can be densely embedded in a compact (at level 0) non-Archimedean approach space Y given by its tower of topologies (S")"2R+ in such a way that at level 0 the compact space (Y; S0) is the Shanin compactification of (X; T0). We give necessary and sufficient conditions for the compactification to be Hausdorff at level 0 and we prove that a space X that is Hausdorff at level 0, ( ; P_ )-regular and ( ; P_ )-normal has such a Hausdorff compactification. 2. P_ -Cat and ( ; P_ )-Cat We follow definitions and notations from [Hofmann, Seal, Tholen (eds.), 2014], unless stated otherwise. In this section we adapt the constructions of P+ -Cat and ( ; P+ )-Cat in [Hofmann, Seal, Tholen (eds.), 2014] to the quantale P_ . Consider the extended real halfline [0; 1] which is a complete lattice with respect to the natural order ≤. We reverse its order, so that 0 = > is the top and 1 = ? is the bottom element. When working with ([0; 1]op; ≤op) and forming infima or suprema we will denote these by infop; Vop; supop or Wop. It means that we will deviate from the conventions made in [Hofmann, Seal, Tholen (eds.), 2014] since we will use both the symbols inf and V when forming infima and sup and W when forming suprema, referring to the natural order on ([0; 1]; ≤). op Since [0; 1] is a chain, it is a frame, and we may consider it a quantale P_ = [0; 1]op; _; 0 with its meet operation (which, according to our conventions, is the supre- mum with respect to the natural order of [0; 1] and will be denoted by _). The map a _ (−): P_ −! P_ is left adjoint to the map a−•(−): P_ −! P_ defined by 0 a ≥ b; a−•b = inffv 2 [0; 1] j b ≤ a _ vg = b a < b: The category P_-Rel has sets as objects and P_ -relations as morphisms. A P_ -relation r : X−!7 Y from X to Y is represented by a map r : X × Y ! P_ . Two P_ -relations r : X−!7 Y and s : Y −!7 Z can be composed in the following way (s · r)(x; z) = inf r(x; y) _ s(y; z) j y 2 Y : 2.1. Definition. P_ -Cat is the category of P_ -spaces (X; a), where X is a set and a : X−!7 X is transitive and reflexive P_ -relation, meaning it is a map a : X × X ! P_ satisfying a(x; y) ≤ a(x; z) _ a(z; y) and a(x; x) = 0 for all x; y; z in X. A morphism f :(X; a) ! (Y; b) of P_ -Cat is a map satisfying b(f(x1); f(x2)) ≤ a(x1; x2) for all x1; x2 in X.
Load more

Recommended publications
  • SOBER APPROACH SPACES 1. Introduction in This Article We Will
    SOBER APPROACH SPACES B. BANASCHEWSKI, R. LOWEN, C. VAN OLMEN 1. Introduction In this article we will introduce the notion of sobriety for approach spaces, modelled after the corresponding familiar concept in the case of topological spaces. Recall that the latter is closely linked to the relationship between the categories Top of topological spaces and Frm of frames, these being certain complete lattices which may be viewed as abstractly defined lat- tices of virtual open sets. More specifically, the connection between these categories is provided by a pair of contravariant functors, adjoint on the right, which assign to each topological space its frame of open subsets and to each frame its spectrum. Sober spaces are then those spaces for which the corresponding adjunction map is a homeomorphism. In the approach setting, the so-called regular function frame of an ap- proach space takes over the role of the frame of open sets in topology and accordingly we introduce an abstractly defined version of this, called an ap- proach frame. This leads to the contravariant functor R from the category AP of approach spaces to AFrm of approach frames and the spectrum func- tor Σ in the opposite direction. R and Σ are then adjoint on the right and an approach space X is called sober if the corresponding adjunction map X → ΣRX is an isomorphism. The purpose of this paper is to give an account of the basic facts con- cerning the functors R and Σ and to present a number of results about sobriety, including its reflectiveness and the relation between sobriety and completeness for uniform approach spaces.
    [Show full text]
  • On X-Normed Spaces and Operator Theory on C 0 Over a Field with A
    ON X-NORMED SPACES AND OPERATOR THEORY ON c0 OVER A FIELD WITH A KRULL VALUATION OF ARBITRARY RANK by Angel Barría Comicheo A thesis submitted to the Faculty of Graduate Studies of The University of Manitoba in partial fulfillment of the requirements of the degree of Doctor of Philosophy Department of Mathematics University of Manitoba Winnipeg Copyright c 2018 by Angel Barría Comicheo Abstract Between 2013 and 2015 Aguayo et al. developed an operator theory on the space c0 of null sequences in the complex Levi-Civita field C by defining an inner product on c0 that induces the supremum norm on c0 and then studying compact and self- adjoint operators on c0, thus presenting a striking analogy between c0 over C and the Hilbert space `2 over C. In this thesis, we try to obtain these results in the most general case possible by considering a base field with a Krull valuation taking values in an arbitrary commutative group. This leads to the concept of X-normed spaces, which are spaces with norms taking values in a totally ordered set X not necessarily embedded in R. Two goals are considered in the thesis: (1) to present and contribute to a theory of X-normed spaces, and (2) to develop an operator theory on c0 over a field with a Krull valuation of arbitrary rank. In order to meet the goal (1), a systematic study of valued fields, G-modules and X-normed spaces is conducted in order to satisfy the generality of the settings required. For the goal (2), we identify the major differences between normed spaces over fields of rank 1 and X-normed spaces over fields of higher rank; and we try to find the right conditions for which the techniques employed in the rank-1 case can be used in the higher rank case.
    [Show full text]
  • Amplicon Analysis I
    Amplicon Analysis I Eduardo Pareja-Tobes, Raquel Tobes Oh no sequences! research group, Era7 Bioinformatics Plaza de Campo Verde, 3, 18001 Granada, Spain September 16, 2019 Abstract Here we present 1. a model for amplicon sequencing 2. a definition of the best assignment of a read to a set of reference sequences 3. strategies and structures for indexing reference sequences and computing the best assign- ments of a set of reads efficiently, based on (ultra)metric spaces and their geometry The models, techniques, and ideas are particularly relevant to scenarios akin to 16S taxonomic profiling, where both the number of reference sequences and the read diversity is considerable. Keywords bioinformatics, NGS, DNA sequencing, DNA sequence analysis, amplicons, ultrametric spaces, in- dexing. Corresponding author Eduardo Pareja-Tobes [email protected] 1 1 Reads, Amplicons, References, Assignments In this section we will define what we understand as reads, amplicons, references, and the best as- signment of a read with respect to a set of references. In our model the reads are a product of the probability distribution for the 4 bases (A, C, G and T) in each position of the sequence. 푛−1 Definition 1.0.1 Read. A read 푅 of length 푛 is a product ∏푖=0 푅푖 of 푛 probability distributions on Σ = {퐴, 푇 , 퐶, 퐺}. We will denote the length of a read as |푅|. The corresponding probability mass function is thus defined on the space Σ푛 of sequences in Σ of 푛−1 푛 length 푛, the domain of 푅. The probability that 푅 assigns to a sequence 푥 = (푥푖)푖=0 ∶ Σ is 푛−1 푅(푥) = ∏ 푅푖(푥푖) 푖=0 Remark 1.0.2.
    [Show full text]
  • Approach Merotopological Spaces and Their Completion
    Hindawi Publishing Corporation International Journal of Mathematics and Mathematical Sciences Volume 2010, Article ID 409804, 16 pages doi:10.1155/2010/409804 Research Article Approach Merotopological Spaces and their Completion Mona Khare and Surabhi Tiwari Department of Mathematics, University of Allahabad, Allahabad 211002, India Correspondence should be addressed to Mona Khare, [email protected] Received 24 July 2009; Accepted 13 April 2010 Academic Editor: Richard Wilson Copyright q 2010 M. Khare and S. Tiwari. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper introduces the concept of an approach merotopological space and studies its category- theoretic properties. Various topological categories are shown to be embedded into the category whose objects are approach merotopological spaces. The order structure of the family of all approach merotopologies on a nonempty set is discussed. Employing the theory of bunches, bunch completion of an approach merotopological space is constructed. The present study is a unified look at the completion of metric spaces, approach spaces, nearness spaces, merotopological spaces, and approach merotopological spaces. 1. Introduction Some of the applications of nearness-like structures within topology are unification, extensions, homology, and connectedness. The categories of R0-topological spaces, uniform spaces 1, 2, proximity spaces 2, 3, and contiguity spaces 4, 5 are embedded into the category of nearness spaces. The study of proximity, contiguity, and merotopic spaces in the more generalized setting of L-fuzzy theory can be seen in 6–13.In14, the notion of an approach space was introduced via different equivalent set of axioms to measure the degree of nearness between a set and a point.
    [Show full text]
  • Arxiv:1810.03128V2 [Math.MG]
    FINITE ULTRAMETRIC BALLS O. DOVGOSHEY Abstract. The necessary and sufficient conditions under which a given family F of subsets of finite set X coincides with the family BX of all balls generated by some ultrametric d on X are found. It is shown that the representing tree of the ultrametric space (BX , dH ) with the Hausdorff distance dH can be obtained from the representing tree TX of ultrametric space (X, d) by adding a leaf to every internal vertex of TX . 1. Introduction. Balls in ultrametric space The main object of research in this paper is the set of all balls in a given finite ultrametric space. The theory of ultrametric spaces is closely connected with various directions of studies in mathematics, physics, linguistics, psychology and computer science. Different prop- erties of ultrametric spaces are described at [3, 7, 11–14, 20,21,28,31– 38,42–46]. The use of trees and tree-like structures gives a natural lan- guage for description of ultrametric spaces. For the relationships between these spaces and the leaves or the ends of certain trees see [1,2,5,8,19,22,23,25–27,38]. In particular, a convenient representa- tion of finite ultrametric spaces (X,d) by monotone canonical trees was found by V. Gurvich and M. Vyalyi [22]. A simple algorithm having a clear geometric interpretation was proposed in [40] for constructing monotone canonical trees. Following [40] we will say that these trees arXiv:1810.03128v2 [math.MG] 23 Mar 2019 are representing trees of spaces (X,d). The present paper can be con- sidered as a development of studies initiated at [22] and continued at [10,16,18,39–41].
    [Show full text]
  • Path Integrals on Ultrametric Spaces by Alan Blair B.Sc, B.A
    I Path Integrals on Ultrametric Spaces by Alan Blair B.Sc, B.A. Hons.) University of Sydney 19885 1989 Submitted to the Department of Mathematics in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology May 1994 1994 Alan Blair. All rights reserved. The author hereby grants to MIT permission to reproduce and to distribute copies of this thesis document in whole or 1n Dart. Signature of, Author. .. A-V . Department of Mat4emati _AprilN. Certified by. ,' Gian-Carlo Rota Professor of Mathematics M.I.T. Thesis Advisor Accepted by . q -. ! .; ".. -. , . 1 - L Scfencp David Vogan Chair DepaTtmental Committee on Graduate Studies iFf.7-7r) t4F7171 AUG 1 994 PATH INTEGRALS ON ULTRAMETRIC SPACES by ALAN BLAIR Submitted to the Department of Mathematics on April 29, 1994 in partial fulfillment of the requirements for the degree of Doctor of Philosophy ABSTRACT A framework for the study of path integrals on ad6lic spaces is developed, and it is shown that a family of path space measures on the localizations of an algebraic number field may, under certain conditions, be combined to form a global path space measure on its ade'le ring. An operator on the field of p-adic numbers analogous to the harmonic oscillator operator is then analyzed, and used to construct an Ornstein-Uhlenbeck type process on the ade'le ring of the rationals. Thesis Advisors: Andrew Lesniewski, Professor of Physics (Harvard) Arthur JaHe, Professor of Mathematics (Harvard) 3 Acknowledgments To my father, who first introduced me to the lofty heights of mathematics, and my mother and brother, who kept me in touch with the real world below.
    [Show full text]
  • MATH 614, Spring 2018 [3Mm] Dynamical Systems and Chaos
    MATH 614 Dynamical Systems and Chaos Lecture 7: Symbolic dynamics (continued). Symbolic dynamics Given a finite set A (an alphabet), we denote by ΣA the set of all infinite words over A, i.e., infinite sequences s =(s1s2 ... ), si ∈A. For any finite word w over the alphabet A, that is, w = s1s2 ... sn, si ∈A, we define a cylinder C(w) to be the set of all infinite words s ∈ ΣA that begin with w. The topology on ΣA is defined so that open sets are unions of cylinders. Two infinite words are considered close in this topology if they have a long common beginning. The shift transformation σ : ΣA → ΣA is defined by σ(s0s1s2 ... )=(s1s2 ... ). This transformation is continuous. The study of the shift and related transformations is called symbolic dynamics. Properties of the shift • The shift transformation σ :ΣA → ΣA is continuous. • An infinite word s ∈ ΣA is a periodic point of the shift if and only if s = www... for some finite word w. • An infinite word s ∈ ΣA is an eventually periodic point of the shift if and only if s = uwww... for some finite words u and w. • The shift σ has periodic points of all (prime) periods. Dense sets Definition. Suppose (X , d) is a metric space. We say that a subset E ⊂ X is everywhere dense (or simply dense) in X if for every x ∈ X and ε> 0 there exists y ∈ E such that d(y, x) <ε. More generally, suppose X is a topological space. We say that a subset E ⊂ X is dense in X if E intersects every nonempty open subset of X .
    [Show full text]
  • Hierarchical Overlapping Clustering of Network Data Using Cut Metrics Fernando Gama, Santiago Segarra, and Alejandro Ribeiro
    IEEE TRANSACTIONS ON SIGNAL AND INFORMATION PROCESSING OVER NETWORKS (ACCEPTED) 1 Hierarchical Overlapping Clustering of Network Data Using Cut Metrics Fernando Gama, Santiago Segarra, and Alejandro Ribeiro Abstract—A novel method to obtain hierarchical and overlap- degrees that may be present. Hierarchical clustering solves ping clusters from network data – i.e., a set of nodes endowed this issue by providing a collection of partitions, indexed with pairwise dissimilarities – is presented. The introduced by a resolution parameter, that can be set by the user to method is hierarchical in the sense that it outputs a nested collection of groupings of the node set depending on the resolution determine the extent up to which nodes are considered similar or degree of similarity desired, and it is overlapping since it or different [9]. In other words, each partition in the collection allows nodes to belong to more than one group. Our construction reflects a different degree of similarity between the nodes, is rooted on the facts that a hierarchical (non-overlapping) ranging from considering all nodes different, to considering clustering of a network can be equivalently represented by all nodes similar. Examples of hierarchical clustering methods a finite ultrametric space and that a convex combination of ultrametrics results in a cut metric. By applying a hierarchical are UPGMA [10], Ward’s method [11], complete [12] or single (non-overlapping) clustering method to multiple dithered versions linkage [13]. of a given network and then convexly combining the resulting However, hierarchical methods still have a major limitation, ultrametrics, we obtain a cut metric associated to the network namely, that nodes are assigned to one and only one category of interest.
    [Show full text]
  • The Range of Ultrametrics, Compactness, and Separability
    The range of ultrametrics, compactness, and separability Oleksiy Dovgosheya,∗, Volodymir Shcherbakb aDepartment of Theory of Functions, Institute of Applied Mathematics and Mechanics of NASU, Dobrovolskogo str. 1, Slovyansk 84100, Ukraine bDepartment of Applied Mechanics, Institute of Applied Mathematics and Mechanics of NASU, Dobrovolskogo str. 1, Slovyansk 84100, Ukraine Abstract We describe the order type of range sets of compact ultrametrics and show that an ultrametrizable infinite topological space (X, τ) is compact iff the range sets are order isomorphic for any two ultrametrics compatible with the topology τ. It is also shown that an ultrametrizable topology is separable iff every compatible with this topology ultrametric has at most countable range set. Keywords: totally bounded ultrametric space, order type of range set of ultrametric, compact ultrametric space, separable ultrametric space 2020 MSC: Primary 54E35, Secondary 54E45 1. Introduction In what follows we write R+ for the set of all nonnegative real numbers, Q for the set of all rational number, and N for the set of all strictly positive integer numbers. Definition 1.1. A metric on a set X is a function d: X × X → R+ satisfying the following conditions for all x, y, z ∈ X: (i) (d(x, y)=0) ⇔ (x = y); (ii) d(x, y)= d(y, x); (iii) d(x, y) ≤ d(x, z)+ d(z,y) . + + A metric space is a pair (X, d) of a set X and a metric d: X × X → R . A metric d: X × X → R is an ultrametric on X if we have d(x, y) ≤ max{d(x, z), d(z,y)} (1.1) for all x, y, z ∈ X.
    [Show full text]
  • A New Approach to the Study of Extended Metric Spaces 1
    Mathematica Aeterna, Vol. 3, 2013, no. 7, 565 - 577 A New Approach to the Study of Extended Metric Spaces Surabhi Tiwari Department of Mathematics Motilal Nehru National Institute of Technology Allahabad, U.P., India. Email: [email protected], [email protected] James F. Peters Computational Intelligence Laboratory Department of Electrical & Computer Engineering University of Manitoba Winnipeg, Manitoba R3T 51-V6, Canada. Email: [email protected] Abstract This paper studies the category theoretic aspects of ε-approach near- ness spaces and ε-approach merotopic spaces, respectively, ε ∈ (0, ∞], which are useful in measuring the degree of nearness (resemblance) of objects. Such structures measure the almost nearness of two collections of subsets of a nonempty set. The categories εANear and εAMer are shown to be full supercategories of various well-known categories, including the category sT op of symmetric topological spaces and con- tinuous maps, and the category Met∞ of extended metric spaces and nonexpansive maps. The results in this paper have important practical implications in the study of patterns in similar pictures. Mathematics Subject Classification: 54E05, 54E17, 54C25. Keywords: Approach merotopy, Nearness space, Topological space. 1 Introduction In [13], the two-argument ε-approach nearness was axiomatized for the pur- pose of presenting an alternative approach for completing extended metric spaces. This completion of extended metric spaces was motivated by the recent work on approach merotopic spaces in [7, 6, 4, 5, 16], (see also [2, 3]). In [15], 566 Surabhi Tiwari and James F. Peters ε-approach nearness was used to prove Niemytzki-Tychonoff theorem for sym- metric topological spaces.
    [Show full text]
  • The Notion of Closedness and D-Connectedness in Quantale
    THE NOTION OF CLOSEDNESS AND D-CONNECTEDNESS IN QUANTALE-VALUED APPROACH SPACES MUHAMMAD QASIM AND SAMED OZKAN¨ Abstract. In this paper, we characterize the local T0 and T1 separa- tion axioms for quantale-valued gauge space, show how these concepts are related to each other and apply them to L-approach space and L- approach system. Furthermore, we give the characterization of a closed point and D-connectedness in quantale-valued gauge space. Finally, we compare all these concepts with other. 1. Introduction Approach spaces have been introduced by Lowen [25, 26] to generalize metric and topological concepts, have many applications in almost all ar- eas of mathematics including probability theory [13], convergence theory [14], domain theory [15] and fixed point theory [16]. Due to its huge im- portance, several generalization of approach spaces appeared recently such as probabilistic approach spaces [18], quantale-valued gauge spaces [19], quantale-valued approach system [20] and quantale-valued approach w.r.t closure operators [24]. Recently, some quantale-valued approach spaces [21] are also characterized by using quantale-valued bounded interior spaces and bounded strong topological spaces which are commonly used by fuzzy math- ematicians. In 1991, Baran [2] introduced local separation axioms and notion of closed- ness in set-based topological categories which are used to define several dis- arXiv:1811.00767v1 [math.GN] 2 Nov 2018 tinct Hausdorff objects [4], T3 and T4 objects [6], regular, completely regular, normed objects [7], notion of compactness and minimality, perfectness [8] and closure operators in the sense of Guili and Dikranjan [17] in some well- known topological categories [9, 10].
    [Show full text]
  • The Missing Link in the Topology-Uniformity-Metric Triad
    Previous Up Next Citations From References: 143 From Reviews: 18 MR1472024 (98f:54002) 54-02 18B30 54Bxx 54Cxx 54Exx Lowen, R. [Lowen, Robert] (B-ANTW) FApproach spaces. The missing link in the topology-uniformity-metric triad. Oxford Mathematical Monographs. Oxford Science Publications. The Clarendon Press, Oxford University Press, New York, 1997. x+253 pp. $110.00. ISBN 0-19-850030-0 FEATURED REVIEW. This book is a landmark in the history of general topology. The author developed approach spaces in a series of papers from 1987 onwards and the book contains the results from those papers, presented in a systematic and definitive manner. Approach spaces form a supercategory of the categories of topological spaces and metric spaces, and the main purpose for their introduction was to fill some gaps concerning categorical aspects of metrizable spaces (see below for details). They not only solved these fundamental problems but also turned out to be interesting objects of study for their own sake. Moreover, they are useful in many areas such as probability theory, functional analysis, function spaces, hyperspaces, and probabilistic metric spaces. They also provide a proper setting for a unified treatment of certain topological and metric properties in the theory of approximation. Let us discuss a motivation. Suppose (X; d) is a metric space and δd(x; A) is the distance between x 2 X and A ⊂ X defined by inffd(x; a): a 2 Ag. We say that x is near A if δd(x; A) = 0. About ninety years back, F. Riesz showed that the concept of a continuous function can be defined by using this nearness relation between points and subsets.
    [Show full text]