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Ramseyan ultrafilters

Lorenz Halbeisen (2001)

Fundamenta Mathematicae

We investigate families of partitions of ω which are related to special coideals, so-called happy families, and give a dual form of Ramsey ultrafilters in terms of partitions. The combinatorial properties of these partition-ultrafilters, which we call Ramseyan ultrafilters, are similar to those of Ramsey ultrafilters. For example it will be shown that dual Mathias forcing restricted to a Ramseyan ultrafilter has the same features as Mathias forcing restricted to a Ramsey ultrafilter. Further we...

Ramsey-like properties for bi-Lipschitz mappings of finite metric spaces

Jiří Matoušek (1992)

Commentationes Mathematicae Universitatis Carolinae

Let ( X , ρ ) , ( Y , σ ) be metric spaces and f : X Y an injective mapping. We put f L i p = sup { σ ( f ( x ) , f ( y ) ) / ρ ( x , y ) ; x , y X , x y } , and dist ( f ) = f L i p . f - 1 L i p (the distortion of the mapping f ). Some Ramsey-type questions for mappings of finite metric spaces with bounded distortion are studied; e.g., the following theorem is proved: Let X be a finite metric space, and let ε > 0 , K be given numbers. Then there exists a finite metric space Y , such that for every mapping f : Y Z ( Z arbitrary metric space) with dist ( f ) < K one can find a mapping g : X Y , such that both the mappings g and f | g ( X ) have distortion at...

Ramsey-type theorems

Gavalec, Martin, Vojtáš, Peter (1980)

Abstracta. 8th Winter School on Abstract Analysis

Random even graphs.

Grimmett, Geoffrey, Janson, Svante (2009)

The Electronic Journal of Combinatorics [electronic only]

Random orderings and unique ergodicity of automorphism groups

Omer Angel, Alexander S. Kechris, Russell Lyons (2014)

Journal of the European Mathematical Society

We show that the only random orderings of finite graphs that are invariant under isomorphism and induced subgraph are the uniform random orderings. We show how this implies the unique ergodicity of the automorphism group of the random graph. We give similar theorems for other structures, including, for example, metric spaces. These give the first examples of uniquely ergodic groups, other than compact groups and extremely amenable groups, after Glasner andWeiss’s example of the group of all permutations...

Random procedures for dominating sets in bipartite graphs

Sarah Artmann, Jochen Harant (2010)

Discussiones Mathematicae Graph Theory

Using multilinear functions and random procedures, new upper bounds on the domination number of a bipartite graph in terms of the cardinalities and the minimum degrees of the two colour classes are established.

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