The Boolean Algebra of Regular Open Sets

1953 ◽  
Vol 5 ◽  
pp. 95-100 ◽  
Author(s):  
R. S. Pierce
Keyword(s):  
Boolean Algebra ◽  
Topological Space ◽  
Distributive Lattice ◽  
Homomorphic Image ◽  
Continuous Functions ◽  
Completely Regular ◽  
Regular Open ◽  
Quasi Ordering

Let S be a completely regular topological space. Let C(S) denote the set of bounded, real-valued, continuous functions on 5. It is well known that C(S) forms a distributive lattice under the ordinary pointwise joins and meets. For any distributive lattice L and any ideal I⊆L, a quasi-ordering of L can be defined as follows : f⊇g if, for all h ∈ L, f ∩ h ∈ I implies g ∩ h ∈ I. If equivalent elements under this quasi-ordering are identified, a homomorphic image of L is obtained.

scholarly journals Lebesgue Measurability of Separately Continuous Functions and Separability

2007 ◽  
Vol 2007 ◽  
pp. 1-4
Author(s):  
V. V. Mykhaylyuk
Keyword(s):  
Topological Space ◽  
Chain Condition ◽  
Continuous Functions ◽  
Negative Answer ◽  
Regular Space ◽  
Property A ◽  
Completely Regular ◽  
Open Set ◽  
Countable Chain Condition ◽  
Countable Chain

A connection between the separability and the countable chain condition of spaces withL-property (a topological spaceXhasL-property if for every topological spaceY, separately continuous functionf:X×Y→ℝand open setI⊆ℝ,the setf−1(I)is anFσ-set) is studied. We show that every completely regular Baire space with theL-property and the countable chain condition is separable and constructs a nonseparable completely regular space with theL-property and the countable chain condition. This gives a negative answer to a question of M. Burke.

scholarly journals Characterizations of Ideals in IntermediateC-RingsA(X)via theA-Compactifications ofX

2013 ◽  
Vol 2013 ◽  
pp. 1-6
Author(s):  
Joshua Sack ◽  
Saleem Watson
Keyword(s):  
Topological Space ◽  
Continuous Functions ◽  
Completely Regular ◽  
Intermediate Ring ◽  
Maximal Ideals ◽  
Kolmogorov Theorem

LetXbe a completely regular topological space. An intermediate ring is a ringA(X)of continuous functions satisfyingC*(X)⊆A(X)⊆C(X). In Redlin and Watson (1987) and in Panman et al. (2012), correspondences𝒵AandℨAare defined between ideals inA(X)andz-filters onX, and it is shown that these extend the well-known correspondences studied separately forC∗(X)andC(X), respectively, to any intermediate ring. Moreover, the inverse map𝒵A←sets up a one-one correspondence between the maximal ideals ofA(X)and thez-ultrafilters onX. In this paper, we define a function𝔎Athat, in the case thatA(X)is aC-ring, describesℨAin terms of extensions of functions to realcompactifications ofX. For such rings, we show thatℨA←mapsz-filters to ideals. We also give a characterization of the maximal ideals inA(X)that generalize the Gelfand-Kolmogorov theorem fromC(X)toA(X).

scholarly journals A GENERALIZATION OF SIERPINSKI THEOREM ON UNIQUE DETERMINING OF A SEPARATELY CONTINUOUS FUNCTION

2021 ◽  
Vol 9 (1) ◽  
pp. 250-263
Author(s):  
V. Mykhaylyuk ◽  
O. Karlova
Keyword(s):  
Continuous Function ◽  
Topological Space ◽  
Dense Subset ◽  
Continuous Functions ◽  
Baire Space ◽  
Regular Space ◽  
Topological Spaces ◽  
Infinite Cardinal ◽  
Urysohn Space ◽  
Completely Regular

In 1932 Sierpi\'nski proved that every real-valued separately continuous function defined on the plane $\mathbb R^2$ is determined uniquely on any everywhere dense subset of $\mathbb R^2$. Namely, if two separately continuous functions coincide of an everywhere dense subset of $\mathbb R^2$, then they are equal at each point of the plane. Piotrowski and Wingler showed that above-mentioned results can be transferred to maps with values in completely regular spaces. They proved that if every separately continuous function $f:X\times Y\to \mathbb R$ is feebly continuous, then for every completely regular space $Z$ every separately continuous map defined on $X\times Y$ with values in $Z$ is determined uniquely on everywhere dense subset of $X\times Y$. Henriksen and Woods proved that for an infinite cardinal $\aleph$, an $\aleph^+$-Baire space $X$ and a topological space $Y$ with countable $\pi$-character every separately continuous function $f:X\times Y\to \mathbb R$ is also determined uniquely on everywhere dense subset of $X\times Y$. Later, Mykhaylyuk proved the same result for a Baire space $X$, a topological space $Y$ with countable $\pi$-character and Urysohn space $Z$. Moreover, it is natural to consider weaker conditions than separate continuity. The results in this direction were obtained by Volodymyr Maslyuchenko and Filipchuk. They proved that if $X$ is a Baire space, $Y$ is a topological space with countable $\pi$-character, $Z$ is Urysohn space, $A\subseteq X\times Y$ is everywhere dense set, $f:X\times Y\to Z$ and $g:X\times Y\to Z$ are weakly horizontally quasi-continuous, continuous with respect to the second variable, equi-feebly continuous wuth respect to the first one and such that $f|_A=g|_A$, then $f=g$. In this paper we generalize all of the results mentioned above. Moreover, we analize classes of topological spaces wich are favorable for Sierpi\'nsi-type theorems.

scholarly journals Density topologies on the plane between ordinary and strong. II

2015 ◽  
Vol 62 (1) ◽  
pp. 13-25
Author(s):  
Elżbieta Wagner-Bojakowska ◽  
Władysław Wilczyński
Keyword(s):  
Topological Space ◽  
Measurable Subset ◽  
Continuous Functions ◽  
Density Point ◽  
Density Topology ◽  
Completely Regular ◽  
The Family

Abstract Let C0 denote a set of all non-decreasing continuous functions f : (0, 1] → (0, 1] such that limx→0+f(x) = 0 and f(x) ≤ x for every x ∊ (0, 1], and let A be a measurable subset of the plane. The notions of a density point of A with respect to f and the mapping defined on the family of all measurable subsets of the plane were introduced in Wagner-Bojakowska, E. Wilcziński, W.: Density topologies on the plane between ordinary and strong, Tatra Mt. Math. Publ. 44 (2009), 139 151. This mapping is a lower density, so it allowed us to introduce the topology Tf , analogously to the density topology. In this note, properties of the topology Tf and functions approximately continuous with respect to f are considered. We prove that (ℝ2, Tf) is a completely regular topological space and we study conditions under which topologies generated by two functions f and g are equal.

Uniformities on a Product

1972 ◽  
Vol 24 (3) ◽  
pp. 379-389 ◽  
Author(s):  
Anthony W. Hager
Keyword(s):  
Topological Space ◽  
Cardinal Number ◽  
Uniform Space ◽  
Continuous Functions ◽  
Topological Spaces ◽  
Infinite Cardinal ◽  
The Real ◽  
Completely Regular

All topological spaces shall be uniformizable (completely regular Hausdorff). A uniformity on X shall be viewed as a collection μ of coverings of X, via the manner of Tukey [20] and Isbell [16], and the associated uniform space denoted μX. Given the uniformizable topological space X, we shall be concerned with compatible uniformities as follows (discussed more carefully in § 1). The fine uniformity α (finest compatible with the topology); the “cardinal reflections“ αm of α (m an infinite cardinal number) ; αc, the weak uniformity generated by the real-valued continuous functions.With μ standing, generically, for one of these uniformities, we consider the question: when is μ(X × Y) = μX × μY For μ = αℵ0 (the finest compatible precompact uniformity), the problem is equivalent to that of whenβ(X × Y) = βX × βY,β denoting Stone-Cech compactification; this is answered by the theorem of Glicksberg [9]. For μ = α, we have Isbell's generalization [16, VI1.32].

scholarly journals The regular open-open topology for function spaces

1996 ◽  
Vol 19 (2) ◽  
pp. 299-302 ◽  
Author(s):  
Kathryn F. Porter
Keyword(s):  
Topological Space ◽  
Continuous Functions ◽  
Function Spaces ◽  
Regular Space ◽  
Spaces Of Continuous Functions ◽  
Regular Open

The regular open-open topology,Troo, is introduced, its properties for spaces of continuous functions are discussed, andTroois compared toToo, the open-open topology. It is then shown thatTrooonH(X), the collection of all self-homeomorphisms on a topological space,(X,T), is equivalent to the topology induced onH(X)by a specific quasi-uniformity onX, whenXis a semi-regular space.

The 𝒞(X,D), a characterization of a Stone almost distributive lattice

2015 ◽  
Vol 08 (03) ◽  
pp. 1550055
Author(s):  
Ch. Santhi Sundar Raj ◽  
K. Rama Prasad ◽  
M. Santhi ◽  
R. Vasu Babu
Keyword(s):  
Distributive Lattice ◽  
Homomorphic Image ◽  
Maximal Element ◽  
Continuous Functions ◽  
Boolean Space

We prove that for any Boolean space [Formula: see text] and a dense Almost Distributive Lattice (ADL) [Formula: see text] with a maximal element, the set [Formula: see text] of all continuous functions of [Formula: see text] into the discrete [Formula: see text] is a Stone ADL. Conversely, it is proved that any Stone ADL is a homomorphic image of [Formula: see text] for a suitable Boolean space [Formula: see text] and a dense ADL [Formula: see text] with a maximal element.

scholarly journals Gelfand theorem implies Stone representation theorem of Boolean rings

1995 ◽  
Vol 18 (4) ◽  
pp. 701-704
Author(s):  
Parfeny P. Saworotnow
Keyword(s):  
Boolean Algebra ◽  
Topological Space ◽  
Representation Theorem ◽  
Compact Hausdorff Space ◽  
Hausdorff Space ◽  
Continuous Functions ◽  
Boolean Rings ◽  
Stone Representation ◽  
Stone Theorem

Stone Theorem about representing a Boolean algebra in terms of open-closed subsets of a topological space is a consequence of the Gelfand Theorem about representing aB∗- algebra as the algebra of continuous functions on a compact Hausdorff space.

scholarly journals Intersections of Primary Ideals in Rings of Continuous Functions

1972 ◽  
Vol 24 (3) ◽  
pp. 502-519 ◽  
Author(s):  
R. Douglas Williams
Keyword(s):  
Topological Space ◽  
Continuous Functions ◽  
Prime Ideals ◽  
Sufficient Condition ◽  
Necessary And Sufficient Condition ◽  
Completely Regular ◽  
Rings Of Continuous Functions ◽  
Necessary And Sufficient ◽  
Primary Ideals

Let C be the ring of all real valued continuous functions on a completely regular topological space. This paper is an investigation of the ideals of C that are intersections of prime or of primary ideals.C. W. Kohls has analyzed the prime ideals of C in [3 ; 4] and the primary ideals of C in [5]. He showed that these ideals are absolutely convex. (An ideal I of C is called absolutely convex if |f| ≦ |g| and g ∈ I imply that f ∈ I.) It follows that any intersection of prime or of primary ideals is absolutely convex. We consider here the problem of finding a necessary and sufficient condition for an absolutely convex ideal I of C to be an intersection of prime ideals and the problem of finding a necessary and sufficient condition for I to be an intersection of primary ideals.

scholarly journals A class of ideals in intermediate rings of continuous functions

2019 ◽  
Vol 20 (1) ◽  
pp. 109 ◽  
Author(s):  
Sagarmoy Bag ◽  
Sudip Kumar Acharyya ◽  
Dhananjoy Mandal
Keyword(s):  
Topological Space ◽  
Continuous Functions ◽  
Alternative Proof ◽  
Prime Ideals ◽  
Borel Sets ◽  
Completely Regular ◽  
Rings Of Continuous Functions ◽  
Intermediate Ring ◽  
The Family ◽  
Established Fact

<p>For  any  completely  regular  Hausdorff  topological  space X,  an  intermediate  ring A(X) of  continuous  functions  stands  for  any  ring  lying between C<sup>∗</sup>(X) and C(X).  It is a rather recently established fact that if A(X) ≠ C(X), then there exist non maximal prime ideals in A(X).We offer an alternative proof of it on using the notion of z◦-ideals.  It is realized that a P-space X is discrete if and only if C(X) is identical to the ring of real valued measurable functions defined on the σ-algebra β(X) of all Borel sets in X.  Interrelation between z-ideals, z◦-ideal and Ʒ<sub>A</sub>-ideals in A(X) are examined.  It is proved that within the family of almost P-spaces X, each Ʒ<sub>A</sub> -ideal in A(X) is a z◦-ideal if and only if each z-ideal in A(X) is a z◦-ideal if and only if A(X) = C(X).</p>

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