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A note on strong negative partition relations

Todd Eisworth (2009)

Fundamenta Mathematicae

We analyze a natural function definable from a scale at a singular cardinal, and use it to obtain some strong negative square-brackets partition relations at successors of singular cardinals. The proof of our main result makes use of club-guessing, and as a corollary we obtain a fairly easy proof of a difficult result of Shelah connecting weak saturation of a certain club-guessing ideal with strong failures of square-brackets partition relations. We then investigate the strength of weak saturation...

Amenability and Ramsey theory

Justin Tatch Moore (2013)

Fundamenta Mathematicae

The purpose of this article is to connect the notion of the amenability of a discrete group with a new form of structural Ramsey theory. The Ramsey-theoretic reformulation of amenability constitutes a considerable weakening of the Følner criterion. As a by-product, it will be shown that in any non-amenable group G, there is a subset E of G such that no finitely additive probability measure on G measures all translates of E equally. The analysis of discrete groups will be generalized to the setting...

An additive decomposition of fuzzy numbers

Dug Hun Hong (2003)


Hong and Do[4] improved Mareš[7] result about additive decomposition of fuzzy quantities concerning an equivalence relation. But there still exists an open question which is the limitation to fuzzy quantities on R (the set of real numbers) with bounded supports in the presented theory. In this paper we restrict ourselves to fuzzy numbers, which are fuzzy quantities of the real line R with convex, normalized and upper semicontinuous membership function and prove this open question.

Chain conditions in maximal models

Paul Larson, Stevo Todorčević (2001)

Fundamenta Mathematicae

We present two m a x varations which create maximal models relative to certain counterexamples to Martin’s Axiom, in hope of separating certain classical statements which fall between MA and Suslin’s Hypothesis. One of these models is taken from [19], in which we maximize relative to the existence of a certain type of Suslin tree, and then force with that tree. In the resulting model, all Aronszajn trees are special and Knaster’s forcing axiom ₃ fails. Of particular interest is the still open question...

Class preserving mappings of equivalence systems

Ivan Chajda (2004)

Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica

By an equivalence system is meant a couple 𝒜 = ( A , θ ) where A is a non-void set and θ is an equivalence on A . A mapping h of an equivalence system 𝒜 into is called a class preserving mapping if h ( [ a ] θ ) = [ h ( a ) ] θ ' for each a A . We will characterize class preserving mappings by means of permutability of θ with the equivalence Φ h induced by h .

Combinatorics of open covers (VII): Groupability

Ljubiša D. R. Kočinac, Marion Scheepers (2003)

Fundamenta Mathematicae

We use Ramseyan partition relations to characterize: ∙ the classical covering property of Hurewicz; ∙ the covering property of Gerlits and Nagy; ∙ the combinatorial cardinal numbers and add(ℳ ). Let X be a T 31 / 2 -space. In [9] we showed that C p ( X ) has countable strong fan tightness as well as the Reznichenko property if, and only if, all finite powers of X have the Gerlits-Nagy covering property. Now we show that the following are equivalent: 1. C p ( X ) has countable fan tightness and the Reznichenko property. 2....

Fragments of strong compactness, families of partitions and ideal extensions

Laura Fontanella, Pierre Matet (2016)

Fundamenta Mathematicae

We investigate some natural combinatorial principles related to the notion of mild ineffability, and use them to obtain new characterizations of mild ineffable and weakly compact cardinals. We also show that one of these principles may be satisfied by a successor cardinal. Finally, we establish a version for κ ( λ ) of the canonical Ramsey theorem for pairs.

Indestructible colourings and rainbow Ramsey theorems

Lajos Soukup (2009)

Fundamenta Mathematicae

We show that if a colouring c establishes ω₂ ↛ [(ω₁:ω)]² then c establishes this negative partition relation in each Cohen-generic extension of the ground model, i.e. this property of c is Cohen-indestructible. This result yields a negative answer to a question of Erdős and Hajnal: it is consistent that GCH holds and there is a colouring c:[ω₂]² → 2 establishing ω₂ ↛ [(ω₁:ω)]₂ such that some colouring g:[ω₁]² → 2 does not embed into c. It is also consistent that 2 ω is arbitrarily large, and there...

Large cardinals and covering numbers

Pierre Matet (2009)

Fundamenta Mathematicae

The paper is concerned with the computation of covering numbers in the presence of large cardinals. In particular, we revisit Solovay's result that the Singular Cardinal Hypothesis holds above a strongly compact cardinal.

More results in polychromatic Ramsey theory

Uri Abraham, James Cummings (2012)

Open Mathematics

We study polychromatic Ramsey theory with a focus on colourings of [ω 2]2. We show that in the absence of GCH there is a wide range of possibilities. In particular each of the following is consistent relative to the consistency of ZFC: (1) 2ω = ω 2 and ω 2 p o l y ( α ) 0 - b d d 2 for every α <ω 2; (2) 2ω = ω 2 and ω 2 p o l y ( ω 1 ) 2 - b d d 2 .

On weaker forms of the chain (F) condition and metacompactness-like covering properties in the product spaces

Süleyman Önal, Çetin Vural (2013)

Open Mathematics

We introduce the concept of a family of sets generating another family. Then we prove that if X is a topological space and X has W = {W(x): x ∈ X} which is finitely generated by a countable family satisfying (F) which consists of families each Noetherian of ω-rank, then X is metaLindelöf as well as a countable product of them. We also prove that if W satisfies ω-rank (F) and, for every x ∈ X, W(x) is of the form W 0(x) ∪ W 1(x), where W 0(x) is Noetherian and W 1(x) consists of neighbourhoods of...

Partition ideals below ω

P. Dodos, J. Lopez-Abad, S. Todorcevic (2012)

Fundamenta Mathematicae

Motivated by an application to the unconditional basic sequence problem appearing in our previous paper, we introduce analogues of the Laver ideal on ℵ₂ living on index sets of the form [ k ] ω and use this to refine the well-known high-dimensional polarized partition relation for ω of Shelah.

Partition properties of subsets of Pκλ

Masahiro Shioya (1999)

Fundamenta Mathematicae

Let κ > ω be a regular cardinal and λ > κ a cardinal. The following partition property is shown to be consistent relative to a supercompact cardinal: For any f : n < ω [ X ] n γ with X P κ λ unbounded and 1 < γ < κ there is an unbounded Y ∪ X with | f ' ' [ Y ] n | = 1 for any n < ω.

Perfect set properties in models of ZF

Carlos Augusto Di Prisco, Franklin C. Galindo (2010)

Fundamenta Mathematicae

We study several perfect set properties of the Baire space which follow from the Ramsey property ω ( ω ) ω . In particular we present some independence results which complete the picture of how these perfect set properties relate to each other.

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