点是Gδ^－集的∑^＊－空间的构成定理

在林寿与我最近合作的一篇文章中指出了∑^*-空间的构成定理需重新考虑．本文就是要证明在空间X的每个点是Gδ^-集的条件下该构成定理是成立的，所得的结论是：X是T1且每个点是Gδ^-集的∑^ -空间，如果f：X→Y是闭的满连续映射，则在Y中有-σ-闭离散子空间Z，使得对每个y∈Y＼Z，f^-1(y)是X的ω1^-紧子空间．为得到该主要结果，本文证明了若空间X是每个点是Gδ^-集的次亚紧空间．则X中的每个闭离散子集是X中的Gδ^-集．     

子空间单位球的逼近紧性

设X是Banach空间,Y为X的子空间,B_X,B_Y分别是X和Y的闭单位球.本文研究B_Y的逼近紧性,证明了B_Y在X中是逼近紧的当且仅当对Y的每个与B_X相交的平移Y_T,Y_T∩B_X在Y_T中都是逼近紧的.还得到B_Y逼近紧的稳定性结果.     

集值映射空间上的■0特征1

应用k-网的概念证明了:若X,Y为■0空间且Y为局部紧的,则X到Y上满足条件(G)的点紧致的族连续集值映射族依紧开拓扑是■0空间.     

单调空间与度量化定理

本文回答了关于MCM空间遗传性的一个问题,讨论了k-MCM空间是k半层空间的条件,得到了一些用g函数刻划的度量化定理.主要结论有:MCM空间是关于Fσ子空间遗传的;在正规空间类中,q空间(ωN空间,k-MCM空间)是关于开Fσ子空间遗传的;如果X是具有Gδ对角线的正则次中紧 k-MCM空间,则X是k半层空间;X是可度量化空间的充要条件是存在X上的g函数满足对X中任意不相交的闭集F与紧集C,都有某个n∈ω,使得(∪x∈F g(n,x))∩(∪y∈C g(n,y))=(?).     

集值映射空间上的(ξ)0特征

应用k-网的概念证明了:若X,Y为(ξ)0空间且Y为局部紧的,则X到Y上满足条件(G)的点紧致的族连续集值映射族依紧开拓扑是(ξ)0空间.     

仿紧性与性质b_1

本文建立关于仿紧性的下列 Alexandroff-urysohn 型特征定理:空间 X 是仿紧的当且仅当 X 的每个良序单调开覆盖有开的局部θ-加细序列.我们还讨论了正紧与点星形正紧性(或离散正紧性)的等价性.     

集值映射空间在紧开拓扑下的NO性质

本文讨论了点紧致的连续集值映射空间在赋予紧开拓扑下的某些拓扑性质,证明了:若X,Y为NO空间,则X到Y上的点紧致的连续集值映射族依紧开拓扑是NO空间,从而将Michael[1]的结论推广到更大的映射空间类上.     

Bnach 空间中远达和同时远达问题的适定性

本文研究Bn ach空间X中远达和同时远达问题的适定性,在集合的Husdorff距离下,对X中的闭凸子集D和相对弱紧的有界闭子集K,证明了下述结果:若D关于K严格凸和有Kdec性质,则D中所有使远达问题mxx,K是适定的点x全体在D中是Gδ型集.作为应用,得到了同时远达问题适定性的类似结果.     

Fuzzy拓扑空间中的紧性(Ⅰ)——定义和特征(英文)

本文在引入了一复盖的概念之后,定义了(?)一紧性,得出了关于闭集中心族,F-网与F-滤子的(?)-紧性的特微,以及A1exander子基定理。并进一步定义了S-紧,L-紧,I-紧和F-紧性,讨论了这些概念之间的关系。设A,B∈I~Y为X中的Fuzzy集,我们称有序对〈A,B〉为X中的一个(?)一集。定义1 设(X,F)是一个Fuzzy拓扑空间,〈A,B〉为X中的一个(?)一开集,P∈P_*(X)。如果〈A,B〉是P的邻域,则我们说〈A,B〉覆盖P。一个开(?)一集族(?)={〈A_λ,B_λ〉:λ∈Λ}称为X的一个(?)-覆盖,当且仅当对于任一P∈IP_*(X),存在λ∈Λ,使〈A_λ,B_λ>覆盖P。定义2 Fuzzy拓扑空间(X,F)称为(?)-紧的,当且仅当每个(?)覆盖都有有限子(?)-覆盖。定理1 Fuzzy拓扑空间(X,F)是(?)-紧的,当且仅当每个闭(?)-集构成的有限中心族都是中心族。定理2 Fuzzy拓扑空间(X,F)是(?)-紧的,当且仅当X中的每个F-网或者(?)-滤子都有聚点。定理5 设S为Fuzzy拓扑空间(X,F)的一个子基,若每个(?)覆盖(?)={〈A_λ,B_λ〉:A_λ,B_λ∈S,λ∈Λ}都有有限子覆盖,则(X,F)是(?)-紧的。     

Banach空间中不适定线性算子方程的最佳逼近解

设X,Y为Banach空间,T为从X到Y的线性算子.T的值域R(T)≠Y且为逼近紧子空间,T的零空间N(T)≠{θ}.证得不适定算子方程Tx=y的最佳逼近解对任意y∈Y均存在的充分必要条件是N(T)为X的迫近子空间.     

Two Notes on Top ological Groups

In this short paper, we firstly give a short proof of Birkhoff-Kakutani Theorem by Moore metrizable Theorem. Then we prove that G is a topological group if it is a paratopological group which is a dense G_δ-set in a locally feebly compact regular space X.     

Stability Characterizations of ε-isometries on Certain Banach Spaces

Suppose that X, Y are two real Banach Spaces. We know that for a standard ε-isometry f : X → Y, the weak stability formula holds and by applying the formula we can induce a closed subspace N of *. In this paper, by using again the weak stability formula, we further show a sufficient and necessary condition for a standard ε-isometry to be stable in assuming that N is w*-closed in Y*.Making use of this result, we improve several known results including Figiel's theorem in reflexive spaces.We also prove that if, in addition, the space Y is quasi-reflexive and hereditarily indecomposable, then L(f)≡span[f(X)] contains a complemented linear isometric copy of X; Moreover, if X =Y, then for every e-isometry f: X → X, there exists a surjective linear isometry S:X → X such that f-S is uniformly bounded by 2ε on X.     

Factorization of mappings of topological spaces and homomorphisms of topological groups in accordance with weight and dimension ind

Symbols w(X), nw(X), and hl(X) denote the weight, the network weight, and the hereditary Lindelöf number of a space X, respectively. We prove the following factorization theorems.

1. Let X and Y be Tychonoff spaces, φ: X→Y a continuous mapping, hl(X)≤τ, and w(Y)≤τ. Then there exist a Tychonoff space Z and continuous mappings ψ: X→Z, χ: Z→Y such that φ=χ o ψ, Z=ψ(X), w(Z)≤τ andind Z≤ind X. Moreover, if nw(X)≤τ, then mapping ψ is one-to-one.
2. Let π: G→H be a continuous homomorphism of a Hausdorff topological group G to a Hausdorff topological group H, hl(G)≤τ and w(H)≤τ. Then there are a Hausdorff topological group G^* and continuous homomorphisms g: G→G^*, h: G^*→H so that π=h o g, G^*=g(G), w(G^*)≤τ andind G^*≤ind G. If nw(G)≤τ, then g is one-to-one.
3. For every continuous mapping φ: X→Y of a regular Lindelöf space X to a Tychonoff space Y one can find a Tychonoff space Z and continuous mappings ψ: X→Z, χ: Z→Y such that φ=χ o ψ, Z=ψ(X), w(Z)≤w(Y),dim Z≤dim X, andind ₀ Z≤ind ₀ X, whereind ₀ is the dimension function defined by V.V.Filippov with the help of G_δ-partitions. If we additionally suppose that X has a countable network, then ψ can be chosen to be one-to-one. The analogous result also holds for topological groups.
4. For each continuous homomorphism π: G→H of a Hausdorff Lindelöf Σ-group G (in particular, of a σ-compact group G) to a Hausdorff group H there exist a Hausdorff group G^* and continuous homomorphisms g: G→G^*, h:G^*→H so that π=h o g, G^*=g(G), w(G^*)≤w(H),dimG^*≤dimG, andind G^*≤ind G. Bibliography: 25 titles.

     

Verallgemeinerungen eines Satzes von S. Piccard

The following result is due to S. Piccard ([12], S.30): “If A,B ?? are Baire sets of second category and if the function f: ?×?→? is defined by f(x,y):=x?y (x,y ε ?), then the interior of f(A×B) is non void”. In this note the two main results assure, that the theorem of S. Piccard remains valid, if (1) ? is replaced by topological spaces X,Y,Z, (2) f:X×Y→Z is a function, which satisfies a certain global (respectively local) solvability condition, (3) A ?X contains a Baire set of second category and (4) B ?Y is only of second category.     

On invariant subspaces for polynomially bounded operators

We discuss the invariant subspace problem of polynomially bounded operators on a Banach space and obtain an invariant subspace theorem for polynomially bounded operators. At the same time, we state two open problems, which are relative propositions of this invariant subspace theorem. By means of the two relative propositions (if they are true), together with the result of this paper and the result of C.Ambrozie and V.Müller (2004) one can obtain an important conclusion that every polynomially bounded operator on a Banach space whose spectrum contains the unit circle has a nontrivial invariant closed subspace. This conclusion can generalize remarkably the famous result that every contraction on a Hilbert space whose spectrum contains the unit circle has a nontrivial invariant closed subspace (1988 and 1997).     

改进的Tsirelson空间TM上的Wigner定理

设X和Y是赋范空间，如果映射f：X→Y满足{||f（x）+f（y）||，||f（x）-f（y）||}={||x+y||，||x-y||}（x，y∈X），则称f是一个相位等距算子.设g，f：X→Y是映射，若存在相位函数ε：X→{-1，1}，使得ε·f=g，则称g和f是相位等价的.本文将证明改进的Tsirelson空间T_M上的任意满相位等距算子均相位等价于一个线性等距算子.该结论同时也给出了改进的Tsirelson空间T_M上的Wigner型定理.     

Spaces in which every dense subset is a Gδ

A topological space X is called a DG_δ-space if every subset of X is a G_δ-set in its closure. In this paper we study DG_δ-spaces that contains subspaces in which every dense subset is open and spaces in which every subset is a G_δ . We give some new results in these classes of topological spaces.     

Über die Gleichstetigkeit von Mengen von linearen Abbildungen und eine Klasse von topologischen linearen Räumen

In the first part of this paper we proof the following theorem: Let E and F be topological linear spaces, α an infinite cardinal number, and H a set of linear mappings from E into F such that every subset G of H with cardinality |G|≤α is equicontinuous. Then H is equicontinuous on every linear subspace of E which is the closed linear hull of a family (B_L;L∈I), |I|≤α, of precompact subsets of E. In the second part we introduce the class of all topological linear spaces E with the following property: A set H of linear mappings from E into a topological linear space is equicontinuous, if every countable subset of H is equicontinuous. We show that this class is closed with respect to forming topological products and linear final topologies.     

Orthogonally Complemented Subspaces in Banach Spaces

In this paper, we extend the Moreau (Riesz) decomposition theorem from Hilbert spaces to Banach spaces. Criteria for a closed subspace to be (strongly) orthogonally complemented in a Banach space are given. We prove that every closed subspace of a Banach space X with dim X ≥ 3 (dim X ≤ 2) is strongly orthognally complemented if and only if the Banach space X is isometric to a Hilbert space (resp. strictly convex), which is complementary to the well-known result saying that every closed subspace of a Banach space X is topologically complemented if and only if the Banach space X is isomorphic to a Hilbert space.     

Interpolation Functors In Weak-Type Interpolation

For interpolation in the diagonal case, i.e. with respect to the two couples (X, X) and (Y, Y), there exists a natural relation between weak-type and strong-type interpolation. Indeed, weak-type interpolation is related to the “M-couples” (ΛX, MX) and (ΛY, MY) of the Lorentz spaces of X and Y. Since ΛZ ? MZ for any space Z, any weak-type interpolation space also has the (strong-type) interpolation property for the “Λ-couples” (ΛX, ΛX) and (ΛY, ΛY). In this paper a scale ${cal G}, c>0$ , of interpolation functors with respect to the Λ-couples is introduced such that all generated interpolation spaces (also) have the weak-type interpolation property. Moreover, we will show that a space is a weak interpolation space if and only if it is generated by one of these functors.