Metrizable Barrelled Countable Enlargements

In 1980, Robertson, Tweddle and Yeomans solved the metrizableBCE problem in certain special cases, for example, in the normablecase under assumption of the Continuum Hypothesis (CH). A completepositive solution was recently given by the author and L. M.Sánchez Ruiz under an assumption, weaker than CH, thatscales exist. A better partial solution for the general BCEproblem obviates scales or other extra-ZFC assumptions, andentirely lays to rest the metrizable BCE problem. The proofstimulates thought about how the least infinite-dimensionalityof normed barrelled spaces impinges on the separable quotientproblem for Banach spaces. 1991 Mathematics Subject Classification46A08.     

Large Cardinals and Ramifiability for Directed Sets

The notion of “ramifiability” (or “tree‐property”), usually applied to cardinals, can be extended to directed sets and is put in relation here with familiar “large cardinal” properties.     

A Note on Hindman-Type Theorems for Uncountable Cardinals

Order - Recent results of Hindman, Leader and Strauss and of Fernández-Bretón and Rinot showed that natural versions of Hindman’s Theorem fail for all uncontable cardinals. On the...     

Stationary Cardinals

Summary This paper will define a new cardinal called aStationary Cardinal. We will show that every weakly ₁ ¹ -indescribable cardinal is a stationary cardinal, every stationary cardinal is a greatly Mahlo cardinal and every stationary set of a stationary cardinal reflects. On the other hand, the existence of such a cardinal is independent of that of a ₁ ¹ -indescribable cardinal and the existence of a cardinal such that every stationary set reflects is also independent of that of a stationary cardinal. As applications, we will show thatV=L implies ¹ holds if is ₁ ¹ -indescribable and so forth.     

Optimal Weyl-type Inequalities for Operators in Banach Spaces

Let (s_n) be an s-number sequence. We show for each k = 1, 2, . . . and n ≥ k + 1 the inequality between the eigenvalues and s-numbers of a compact operator T in a Banach space. Furthermore, the constant (k + 1)^1/2 is optimal for n = k + 1 and k = 1, 2, . . .. This inequality seems to be an appropriate tool for estimating the first single eigenvalues. On the other hand we prove that the Weyl numbers form a minimal multiplicative s-number sequence and by a well-known inequality between eigenvalues and Weyl numbers due to A. Pietsch they are very good quantities for investigating the optimal asymptotic behavior of eigenvalues. Research of the second author was supported by the DFG Emmy-Noether grant Hi 584/2-3.     

Optimal Interpolating Spaces Preserving Shape

In this paper we study the existence and characterization of spaces which are images of minimal-norm projections that are required to interpolate at given functionals and satisfy additional shape-preserving requirements. We will call such spaces optimal interpolating spaces preserving shape. This investigation leads to concrete solutions in classical settings and, as examples, Π_n will be determined to be such spaces with regard to certain interpolation and shape-preserving requirements on the projections. Restated, the theory of this paper gives rist to an n-dimensional Hahn–Banach extension theorem, where the minimal-norm extension is required to keep invariant a fixed cone.     

Finsler vector bundles -- Metrizable connections

Periodica Mathematica Hungarica -     

大基数与Chang氏模型C

本文研究了一些基数在Ｃｈａｎｇ氏模型Ｃ中的存在性，证明发如下结果：（１）如果Ｋ是弱紧基数，则Ｋ在Ｃ中也是弱紧基数，（２）如果Ｋ是ｉｎｅｆｆａｂｌｅ基数，则Ｋ在Ｃ中也是ｉｎｅｆｆａｂｌｅ基数。（３）如果Ｋ是完全ｉｎｅｆｆａｂｌｅ基数，则Ｋ在Ｃ中也是完全ｉｎｅｆｆａｂｌｅ基数。（４）设Ｊ：Ｃ→Ｃ为初等嵌入，Ｋ为最小变动的基数，则Ｋ在Ｃ中完全ｉｎｅｆｆａｂｌｅ基数，且是完全Ｒａｍｓｅｙ基数。     

Weak Covering at Large Cardinals

We show that weakly compact cardinals are the smallest large cardinals k where k⁺ < k⁺ is impossible provided 0^# does not exist. We also show that if k^+Kc < k⁺ for some k being weakly compact (where K^c is the countably complete core model below one strong cardinal), then there is a transitive set M with M ? ZFC + “there is a strong cardinal”.     

Barrelled spaces with a B-complete completion

Let (E, ) be a barrelled locally convex space. The aim of this paper is to describe the barrelled topologies on E weaker than . When the completion Ê of (E, ) is B-complete, various properties of the barrelled topologies weaker than are proved. Some examples are given to illustrate the possible situations.     

Optimal Sobolev Type Inequalities in Lorentz Spaces

It is well known that the classical Sobolev embeddings may be improved within the framework of Lorentz spaces L ^p,q : the space $\mathcal{D}^{1,p}(\mathbb R^n)$ , 1?<?p?<?n, embeds into $L^{p^*,q}(\mathbb R^n)$ , p?≤?q?≤?∞. However, the value of the best possible embedding constants in the corresponding inequalities is known just in the case $L^{p^*,p}(\mathbb R^n)$ . Here, we determine optimal constants for the embedding of the space $\mathcal{D}^{1,p}(\mathbb R^n)$ , 1?<?p?<?n, into the whole Lorentz space scale $L^{p^{\ast}, q}(\mathbb R^n)$ , p?≤?q?≤?∞, including the limiting case q?=?p of which we give a new proof. We also exhibit extremal functions for these embedding inequalities by solving related elliptic problems.     

A partition relation for successors of Large Cardinals

We address partition problems of Erd?s and Hajnal by showing that for all , if and carries a -dense ideal. If is measurable we show that for where is a very large ordinal less than that is closed under all primitive recursive ordinal operations. Received: 27 June 2001 / Revised version: 5 December 2001 / Published online: 4 February 2003 The first author was partially supported by NSF grant DMS-0101155 and the Equipe d'Analyse Univ. of Paris 6. The second author was partially supported by NSF grants DMS-0072560 and DMS-9704477.     

Optimal Convergence Rates Results for Linear Inverse Problems in Hilbert Spaces

In this article, we prove optimal convergence rates results for regularization methods for solving linear ill-posed operator equations in Hilbert spaces. The results generalizes existing convergence rates results on optimality to general source conditions, such as logarithmic source conditions. Moreover, we also provide optimality results under variational source conditions and show the connection to approximative source conditions.     

Optimal Subspaces for n -Widths of Bounded Subsets in Hilbert Spaces

In this article, we consider the problem of proving the optimality of several approximation spaces by means of n-widths. Specifically, they are optimal subspaces for approximating bounded subsets in some Hilbert spaces with mesh-dependent norms. We prove that finite element spaces and newly developed generalized L-spline spaces are optimal subspaces for n-widths.     

Metrizable extensions of dynamical systems from function algebras

Peters and Pennings introduced and studied in [9] and [11] a kind of extensions of dynamical systems induced by certain C^*-algebras, which they calltame extensions. In this paper we study the behaviour of metrizable tame extensions when some of the most important dynamical concepts related to the metric (such as sources, sinks, saddles, the shadowing property and distallity) are considered. We will confirm that these extensions can be troublesome in this context. We show, however, that sources and sinks are preserved under certain conditions. Entrata in Redazione il 24 febbraio 1997. Research partially supported by Generalitat Valenciana, (2223/94).     

Witnessing numbers of Shelah Cardinals

We consider minimal ranks of extenders associated with Shelah cardinals by introducing witnessing numbers. Using these numbers we shall investigate effects of Shelah cardinals above themselves. MSC: 03E55.