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On the connectedness of boundary and complement for domains

Andrzej Czarnecki, Marcin Kulczycki, Wojciech Lubawski (2011)

Annales Polonici Mathematici

This article gives a short and elementary proof of the fact that the connectedness of the boundary of an open domain in ℝⁿ is equivalent to the connectedness of its complement.

On the continuity of the elements of the Ellis semigroup and other properties

Salvador García-Ferreira, Yackelin Rodríguez-López, Carlos Uzcátegui (2021)

Commentationes Mathematicae Universitatis Carolinae

We consider discrete dynamical systems whose phase spaces are compact metrizable countable spaces. In the first part of the article, we study some properties that guarantee the continuity of all functions of the corresponding Ellis semigroup. For instance, if every accumulation point of X is fixed, we give a necessary and sufficient condition on a point a X ' in order that all functions of the Ellis semigroup E ( X , f ) be continuous at the given point a . In the second part, we consider transitive dynamical...

On the continuity of the pressure for monotonic mod one transformations

Peter Raith (2000)

Commentationes Mathematicae Universitatis Carolinae

If f : [ 0 , 1 ] is strictly increasing and continuous define T f x = f ( x ) ( mod 1 ) . A transformation T ˜ : [ 0 , 1 ] [ 0 , 1 ] is called ε -close to T f , if T ˜ x = f ˜ ( x ) ( mod 1 ) for a strictly increasing and continuous function f ˜ : [ 0 , 1 ] with f ˜ - f < ε . It is proved that the topological pressure p ( T f , g ) is lower semi-continuous, and an upper bound for the jumps up is given. Furthermore the continuity of the maximal measure is shown, if a certain condition is satisfied. Then it is proved that the topological pressure is upper semi-continuous for every continuous function g : [ 0 , 1 ] , if and only if 0 is...

On the convergence and character spectra of compact spaces

István Juhász, William A. R. Weiss (2010)

Fundamenta Mathematicae

An infinite set A in a space X converges to a point p (denoted by A → p) if for every neighbourhood U of p we have |A∖U| < |A|. We call cS(p,X) = |A|: A ⊂ X and A → p the convergence spectrum of p in X and cS(X) = ⋃cS(x,X): x ∈ X the convergence spectrum of X. The character spectrum of a point p ∈ X is χS(p,X) = χ(p,Y): p is non-isolated in Y ⊂ X, and χS(X) = ⋃χS(x,X): x ∈ X is the character spectrum of X. If κ ∈ χS(p,X) for a compactum X then κ,cf(κ) ⊂ cS(p,X). A selection of our results (X...

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