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Amenability and unique ergodicity of automorphism groups of Fraïssé structures

Andy Zucker (2014)

Fundamenta Mathematicae

In this paper we consider those Fraïssé classes which admit companion classes in the sense of [KPT]. We find a necessary and sufficient condition for the automorphism group of the Fraïssé limit to be amenable and apply it to prove the non-amenability of the automorphism groups of the directed graph S(3) and the boron tree structure T. Also, we provide a negative answer to the Unique Ergodicity-Generic Point problem of Angel-Kechris-Lyons [AKL]. By considering G L ( V ) , where V is the countably infinite-dimensional...

An abstract version of Sierpiński's theorem and the algebra generated by A and CA functions

J. Cichoń, Michał Morayne (1993)

Fundamenta Mathematicae

We give an abstract version of Sierpiński's theorem which says that the closure in the uniform convergence topology of the algebra spanned by the sums of lower and upper semicontinuous functions is the class of all Baire 1 functions. Later we show that a natural generalization of Sierpiński's result for the uniform closure of the space of all sums of A and CA functions is not true. Namely we show that the uniform closure of the space of all sums of A and CA functions is a proper subclass of the...

An answer to a question of Arhangel'skii

Henryk Michalewski (2001)

Commentationes Mathematicae Universitatis Carolinae

We prove that there exists an example of a metrizable non-discrete space X , such that C p ( X × ω ) l C p ( X ) but C p ( X × S ) ¬ l C p ( X ) where S = ( { 0 } { 1 n + 1 : n ω } ) and C p ( X ) is the space of all continuous functions from X into reals equipped with the topology of pointwise convergence. It answers a question of Arhangel’skii ([2, Problem 4]).

An answer to a question of Cao, Reilly and Xiong

Zafer Ercan, S. Onal (2006)

Czechoslovak Mathematical Journal

We present a simple proof of a Banach-Stone type Theorem. The method used in the proof also provides an answer to a conjecture of Cao, Reilly and Xiong.

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