On Λ-generalized closed sets in topological spaces

We introduce new classes of sets called Λ _g -closed sets and Λ _g -open sets in topological spaces. We also investigate several properties of such sets. It turns out that Λ _g -closed sets and Λ _g -open sets are weaker forms of closed sets and open sets, respectively and stronger forms of g-closed sets and g-open sets, respectively. Dedicated to Professor Maximilian Ganster on the occasion of his 50th birthday     

Köthe spaces and topological algebra with bases

Nuclear Köthe sequence spaceλ(P) its crossdualλ(P) ^x and their non-nuclear variants are examined as topological algebras. Modelling on them, a general theory of nuclear topological algebras with orthogonal basis is developed. As a by-product, abstract characterizations of sequence algebras ?^∞ andc ₀ are obtained. In a topological algebra set-up, an abstract Grothendieck-Pietsch nuclearity criterion is developed.     

Convexification in locally pseudo-convex algebras

We show that the convexified topology of a locally pseuod-convex algebra can be determined by an explicit family of seminorms. A natural relationship between some properties of locally pseudo-convex algebras and the associated locally convex algebras obtained by convexification is also established.     

On Well-posed Mutually Nearest and Mutually Furthest Point Problems in Banach Spaces

Let G be a non-empty closed(resp．bounded closed)boundedly relatively weakly compact subset in a strictly convex Kadec Banach space X．Let K(X)denote the space of all non-empty compact convex subsets of X endowed with the Hausdorff distance．Moreover,let KG(X)denote the closure of the set {A∈K(x)：A∩G=0}．We prove that the set of all A∈KG(X)(resp．A∈K(X)),such that the minimization (resp．maximization)problem min(A,G)(resp．max(A,G))is well posed,contains a dense Gδ-subset of KG(X)(resp．K(X))．thus extending the recent results due to Blasi,Myjak and Papini and Li．     

Product of lattice-valued measures on topological spaces

X ₁ and X ₂ are completely regular Hausdorff spaces, E ₁, E ₂ and F are Dedekind complete Banach lattices, 〈·,·〉: E ₁ × E ₂ → F is a bilinear mapping, and μ ₁ and μ ₂ are, respectively, E ₁ and E ₂ valued positive, countably additive Baire or Borel measures (countable additivity relative to order convergence) on X ₁ and X ₂. Under certain conditions the existence and uniqueness of the F-valued, positive, product measure is proved.      

On the K0 groups of nest algebras

In this paper we compute the K ₀ group of any nest subalgebra of ().     

Typical ℤn-actions can be inserted only in injective ℝn-actions

We study actions of the groups ?ⁿ and ?ⁿ by Lebesgue space automorphisms. We prove that a typical ?ⁿ-action can be inserted only in injective actions of ?ⁿ, n ∈ ?. We give a simple proof of the fact that a typical ?²-action cannot be inserted in an ?-action.     

On a Possible Continuous Analogue of the Szpilrajn Theorem and its Strengthening by Dushnik and Miller

The Szpilrajn theorem and its strengthening by Dushnik and Miller belong to the most quoted theorems in many fields of pure and applied mathematics as, for instance, order theory, mathematical logic, computer sciences, mathematical social sciences, mathematical economics, computability theory and fuzzy mathematics. The Szpilrajn theorem states that every partial order can be refined or extended to a total (linear) order. The theorem by Dushnik and Miller states, moreover, that every partial order is the intersection of its total (linear) refinements or extensions. Since in mathematical social sciences or, more general, in any theory that combines the concepts of topology and order one is mainly interested in continuous total orders or preorders in this paper some aspects of a possible continuous analogue of the Szpilrajn theorem and its strengthening by Dushnik and Miller will be discussed. In particular, necessary and sufficient conditions for a topological space to satisfy a possible continuous analogue of the Dushnik-Miller theorem will be presented. In addition, it will be proved that a continuous analogue of the Szpilrajn theorem does not hold in general. Further, necessary and in some cases necessary and sufficient conditions for a topological space to satisfy a possible continuous analogue of the Szpilrajn theorem will be presented.      

Notes on symmetric g-functions

A number of generalized metric spaces have been defined or characterized in terms of g-functions. Symmetric g-functions are discussed by C. Good, D. Jennings and A. M. Mohamad. In this paper, some questions about symmetric g-functions are answered, particularly it is shown that every sym-wg-space is expandable. The project is supported by the NNSF (10571151) and NSF (2006J0397) of Fujian Province of China.     

Well-Embedding and G δ -Density in a Pointfree Setting

Translating the notion of G _δ -dense and well-embedded subspaces into a pointfree setting gives some elegant results (with remarkably simple proofs), most notably how the two concepts are related – a fact which, no doubt, is well-known to classical topologists, but is easily overlooked.     

On generalized neighbourhood systems

It is shown in the paper [1] that every generalized topology can be generated by a generalized neighbourhood system. Following the paper [3], we discuss some questions related to this construction. Research supported by Hungarian Foundation for Scientific Research, grant No. T 49786.     

On the Schwartz space isomorphism theorem for rank one symmetric space

In this paper we give a simpler proof of the L ^p -Schwartz space isomorphism (0 < p ≤ 2) under the Fourier transform for the class of functions of left δ-type on a Riemannian symmetric space of rank one. Our treatment rests on Anker’s [2] proof of the corresponding result in the case of left K-invariant functions on X. Thus we give a proof which relies only on the Paley-Wiener theorem.     

On the communication complexity oft-intersection problems in generalized Boolean algebras

We consider the following game: Two players independently choose a chain in a partially ordered set. How many bits of information have to be communicated until at least one of the players knows whether the chains have exactlyt elements in common? This model generalizes thet-intersection problem for subsets of a finite set. We establish the deterministic communication complexity in general. For the special cases of generalized Boolean algebras, we present improved nondeterministic and probabilistic protocols that are of optimal order of complexity for classes with fixed widthq.     

On two questions of the theory of retracts

We establish that condition (Γ) on brick decomposition is indecomposable. This answers K. Borsuk’s question [1]. We prove that there exist metric spaces X and Y and a point (a, b) ∈ X × Y such that (a, b) is an r-point of the product X × Y; moreover, a is not an r-point of X. This answers A. Kosinski’s question [2].     

On the γ n -complete hypergroups and K H hypergroups

The class of γn-complete hypergroups is introduced. Several properties and examples are found both of γn-complete hypergroups and of KH hypergroups.     

On non-isotropic harmonic maps of surfaces into complex projective spaces

It is proved by purely algebraic method that weakly conformai, conformai andA _z ³ = 0 are mutually equivalent if ϕ :Ω→ℂP ⁿ is a non-isotropic harmonic map and the harmonic maps with isotropy order ≥3 are uniquely determined by a system of ordinary differential equations. A method is given, by which the isotropy orders of non-isotropic harmonic maps can be computed.     

Enlargements and generalized topologies

The paper discusses the generalization of a construction described in [6] for the case when the starting point topology is replaced by a generalized topology. Research supported by Hungarian Foundation for Scientific Research, grant No. T 49786.