A polarized partition relation for cardinals of countable cofinality

We prove that if and , then

for all . This polarized partition relation holds if for every partition either there are and with or there are and with .

     

Universal indestructibility for degrees of supercompactness and strongly compact cardinals

We establish two theorems concerning strongly compact cardinals and universal indestructibility for degrees of supercompactness. In the first theorem, we show that universal indestructibility for degrees of supercompactness in the presence of a strongly compact cardinal is consistent with the existence of a proper class of measurable cardinals. In the second theorem, we show that universal indestructibility for degrees of supercompactness is consistent in the presence of two non-supercompact strongly compact cardinals, each of which exhibits a significant amount of indestructibility for its strong compactness. The first author’s research was partially supported by PSC-CUNY grants and CUNY Collaborative Incentive grants. The first author wishes to thank James Cummings for helpful discussions on the subject matter of this paper. In addition, both authors wish to thank the referee, for many helpful comments and suggestions which were incorporated into the current version of the paper.     

Calculus on strong partition cardinals

In [1] it was shown that if κ is a strong partition cardinal, then every function from [κ ]^κ to [κ ]^κ is continuous almost everywhere. In this investigation, we explore whether such functions are differentiable or integrable in any sense. Some of them are. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A weird relation between two cardinals

For a set M, let \({\text {seq}}(M)\) denote the set of all finite sequences which can be formed with elements of M, and let \([M]^2\) denote the set of all 2-element subsets of M. Furthermore, for a set A, let Open image in new window denote the cardinality of A. It will be shown that the following statement is consistent with Zermelo–Fraenkel Set Theory \(\textsf {ZF}\): There exists a set M such that Open image in new window and no function Open image in new window is finite-to-one.     

A chain compact space which is not strongly scattered

A compactT ₂ spaceX which is separable, scattered and uncountable, but still so thatX ^α−X^α+1is countable for all α∈[1, ω) is constructed. This answers one of the problems presented by M. E. Rudin in a conference as an open problem and attributed by her to Telgarsky. The author acknowledges a faculty research grant from Memphis State University when this paper was written.     

A partition relation for partially ordered sets

We introduce a partition relation which is an alternate for measuring how badly the ordinary partition relation fails, we develop its corresponding partition calculus and we determine its status for various typical partially ordered sets.     

On the least strongly compact cardinal

We prove that under the assumption of a supercompact cardinal κ which is a limit of supercompact cardinals, for any increasing Σ₂ function φ the set {∂<κ:∂ is at least φ(∂) supercompact, is strongly compact, yet is not fully supercompact} is unbounded in κ. We then use ideas of Magidor to show that under the hypotheses of a supercompact cardinal which is a limit of supercompact cardinals it is consistent for the least strongly compact cardinal κ₀ to be at least φ(κ₀) supercompact yet not to be fully supercompact, where φ is again an increasing Σ₂ function which also meets certain other technical restrictions. The author wishes to thank Menachem Magidor for helpful conversations and suggestions in method which were used in the proof of Theorem 2.     

Σ‐algebraically compact modules and ‐compact cardinals

We prove that the property characterizes Σ‐algebraically compact modules if is not ω‐measurable. Moreover, under a large cardinal assumption, we show that over any ring R where is not ω‐measurable, any free module M of ω‐measurable rank satisfies , hence the assumption on cannot be dropped in general (e.g., over small non‐right perfect rings). In this way, we extend results from a recent paper by Simion Breaz 4 .     

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.     

A cardinal defined by a polarized partition relation

We study the first cardinalκ satisfying a partition relation defined on the set of finite sequences of smaller ordinals. We show that the fact that this cardinal is ℵ_ω is equiconsistent with the existence of a measurable cardinal. Under GCH, this cardinal must be inaccessible if it has uncountable cofinality. It is shown that the GCH assumption is necessary here.     

Small compact perturbation of strongly irreducible operators

An operatorT onH is called strongly irreducible ifT is not similar to any reducible operators. In this paper, we shall say yes to answer the following question raised by D. A. Herrero.Given an operatorT with connected spectrum (T) and a positive number , can we find a compact operatorK with K < such thatT+K is strongly irreducible?Supported by National Natural Science Foundation of China(19901011), Mathematical Center of State Education Commission of China and 973 Project of China     

Quasitriangular + small compact = strongly irreducible

Let be a bounded linear operator acting on a separable infinite dimensional Hilbert space. Let be a positive number. In this article, we prove that the perturbation of by a compact operator with can be strongly irreducible if is a quasitriangular operator with the spectrum connected. The Main Theorem of this article nearly answers the question below posed by D. A. Herrero.

Suppose that is a bounded linear operator acting on a separable infinite dimensional Hilbert space with connected. Let be given. Is there a compact operator with such that is strongly irreducible?

     

A canonical partition relation for finite subsets of ω

We prove a canonical partition relation for finite subsets of ω that generalizes Hindman's theorem in much the same way that the Erdös-Rado canonical partition relation generalizes Ramsey's theorem. As an application of this we establish a generalized pigeon-hole principle for infinite dimensional vector spaces over the two element field.     

Yang-Mills connections over compact strongly pseudoconvex CR manifolds

Dedicated to Professor Noboru Tanaka in his sixtieth birthday     

A combinatorial property of cardinals

(GCH) For every cardinal there exists such that for every , there are such that .

     

A few remarks on Rowbottom cardinals

It is proved that every regular Rowbottom cardinal which is greater than the continuum is strongly inaccessible. We notice that the theory “ZFC + every cardinal of cofinality ω is Rowbottom” is inconsistent. This answers a question raised by C. C. Chang and H. J. Keisler.     

Colouring without triangles and partition relation

We solved questions of Erdös and Hajnal and deal with related topics. In particular, we show (CH) that in an example ofN→[N] ₃ ² , there need not be a triangle with three colours.