（LF）-空间的完备性

设（E，ξ）=indlim（E．，ξn）为Frechel空间序列的诱导权限，我们证明了：若每个（Enξ|En）正速完备，则（E，ξ）=indlim（En，ξn）为完备，进而证明了；若对于每个自然数n，存在自然数m（n）使对于任意p≥m（n）有En；则（E，ξ）为完备．     

On square roots of isometries

Abstract

In various normed spaces we answer the question of when a given isometry is a square of some isometry. In particular, we consider (real and complex) matrix spaces equipped with unitarily invariant norms and unitary congruence invariant norms, as well as some infinite dimensional spaces illustrating the difference between finite and infinite dimensions.     

On extension of isometries and approximate isometries between unit spheres

In this paper, we will study the isometric extension problem for L¹-spaces and prove that every surjective isometry from the unit sphere of L¹(μ) onto that of a Banach space E can be extended to a linear surjective isometry from L¹(μ) onto E. Moreover, we introduce the approximate isometric extension problem and show that, if E and F are Banach spaces and E satisfies the property (m) (special cases are L^∞(Γ), C₀(Ω) and L^∞(μ)), then every bijective ?-isometry between the unit spheres of E and F can be extended to a bijective 5?-isometry between their closed unit balls. At last, we will give an example to show that the surjectivity assumption cannot be omitted. Using this, we solve the non-surjective isometric extension problem in the negative.     

Asymptotic properties of isometries

In this paper, we prove two theorems on the local stability of isometries in connection with (ε,p)-isometries. These theorems reveal that a large class of (ε,p)-isometries, defined on various restricted domains, are stable.     

On extension theory inL 2-spaces

We present the first steps towards a general extension theory inL ²-spaces. By this theory it is possible to construct all perturbations of the Laplacian supported by a closed setN even if the classical capacity ofN equals zero.     

On Some Problems of Grothendieck Concerning (F) and (DF) Spaces

This is an expository article devoted to the answers to the 10 open problems of the fundamental paper of Grothendieck (Summa Res. Math. 1954; 3:57–123), some of which were given in the recent years.     

A note on isometries of Lipschitz spaces

The main purpose of this article is to generalize a recent result about isometries of Lipschitz spaces. Botelho, Fleming and Jamison [2] described surjective linear isometries between vector-valued Lipschitz spaces under certain conditions. In this article, we extend the main result of [2] by removing the quasi-sub-reflexivity condition from Banach spaces.     

On the completion of (LF)-spaces

Once the existence of metrizable (LF)-spaces was discovered, the problem whether the completion of an (LF)-space is or is not an (LF)-space was answered in the negative, because no (LF)-space can be a Fréchet space. However, some (non-metrizable) (LF)-spaces are complete, e.g. the classical Köthe's strict (LF)-spaces. In this paper we will carry out a thorough study of the completeness of (LF)-spaces stressing upon the stable completion properties of (LB)-spaces. A basic tool for handling this problem is an Open Mapping Theorem for completions of (LF)-spaces, which is also proved in the present paper.This research, supported by a Fulbright-MEC fellowship, was carried out during the author's visit at the University of Maryland while on leave from the University of Extremadura. The author is grateful to Professor S. A. Saxon for very helpful conversation and, especially, for calling his attention to the problem of completions of (LF)-spaces.     

A fixed point approach to the stability of isometries

In this paper, we apply a fixed point theorem to the proof of Hyers-Ulam-Rassias stability property for isometries from a normed space into a Banach space, in which the parallelogram law holds.     

A remark on extension of into isometries

In this paper, we prove that an into isometry form S（l（n）^∞） to S（E）, which under some conditions, can be extended to be a linear isometry defined on the whole space. Therefore we improve the results of [Ding, G. G.： The isometric extension of an into mapping from the unit sphere S（l（2）^∞） to S（Lμ^1）. Acta Mathematica Sinica, English Series, 22（6）, 1721-1724 （2006）].     

The property (MLUR) in symmetric (KB)-spaces

Translated from Matematicheskie Zametki, Vol. 52, No. 6, pp. 149–151, December, 1992.