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On continuity of measurable group representations and homomorphisms

Yulia Kuznetsova (2012)

Studia Mathematica

Let G be a locally compact group, and let U be its unitary representation on a Hilbert space H. Endow the space ℒ(H) of bounded linear operators on H with the weak operator topology. We prove that if U is a measurable map from G to ℒ(H) then it is continuous. This result was known before for separable H. We also prove that the following statement is consistent with ZFC: every measurable homomorphism from a locally compact group into any topological group is continuous.

On continuous actions commutingwith actions of positive entropy

Mark Shereshevsky (1996)

Colloquium Mathematicae

Let F and G be finitely generated groups of polynomial growth with the degrees of polynomial growth d(F) and d(G) respectively. Let S = S f f ∈ F be a continuous action of F on a compact metric space X with a positive topological entropy h(S). Then (i) there are no expansive continuous actions of G on X commuting with S if d(G)

On convergence theory in fuzzy topological spaces and its applications

Nouh, Ali Ahmed (2005)

Czechoslovak Mathematical Journal

In this paper we introduce and study new concepts of convergence and adherent points for fuzzy filters and fuzzy nets in the light of the Q -relation and the Q -neighborhood of fuzzy points due to Pu and Liu [28]. As applications of these concepts we give several new characterizations of the closure of fuzzy sets, fuzzy Hausdorff spaces, fuzzy continuous mappings and strong Q -compactness. We show that there is a relation between the convergence of fuzzy filters and the convergence of fuzzy nets similar...

On countable dense and strong n-homogeneity

Jan van Mill (2011)

Fundamenta Mathematicae

We prove that if a space X is countable dense homogeneous and no set of size n-1 separates it, then X is strongly n-homogeneous. Our main result is the construction of an example of a Polish space X that is strongly n-homogeneous for every n, but not countable dense homogeneous.

On countable families of sets without the Baire property

Mats Aigner, Vitalij A. Chatyrko, Venuste Nyagahakwa (2013)

Colloquium Mathematicae

We suggest a method of constructing decompositions of a topological space X having an open subset homeomorphic to the space (ℝⁿ,τ), where n is an integer ≥ 1 and τ is any admissible extension of the Euclidean topology of ℝⁿ (in particular, X can be a finite-dimensional separable metrizable manifold), into a countable family ℱ of sets (dense in X and zero-dimensional in the case of manifolds) such that the union of each non-empty proper subfamily of ℱ does not have the Baire property in X.

On dense subspaces satisfying stronger separation axioms

Ofelia Teresa Alas, Mihail G. Tkachenko, Vladimir Vladimirovich Tkachuk, Richard Gordon Wilson, Ivan V. Yashchenko (2001)

Czechoslovak Mathematical Journal

We prove that it is independent of ZFC whether every Hausdorff countable space of weight less than c has a dense regular subspace. Examples are given of countable Hausdorff spaces of weight c which do not have dense Urysohn subspaces. We also construct an example of a countable Urysohn space, which has no dense completely Hausdorff subspace. On the other hand, we establish that every Hausdorff space of π -weight less than 𝔭 has a dense completely Hausdorff (and hence Urysohn) subspace. We show that...

On Diviccaro, Fisher and Sessa open questions

Ljubomir B. Ćirić (1993)

Archivum Mathematicum

Let K be a closed convex subset of a complete convex metric space X and T , I : K → K two compatible mappings satisfying following contraction definition: T x , T y ) ≤ ( I x , I y ) + ( 1 - a ) max { I x . T x ) , I y , T y ) } for all x , y in K , where 0 < a < 1 / 2 p - 1 and p ≥ 1 . If I is continuous and I ( K ) contains [ T ( K ) ] , then T and I have a unique common fixed point in K and at this point T is continuous. This result gives affirmative answers to open questions set forth by Diviccaro, Fisher and Sessa in connection with necessarity of hypotheses of linearity and non-expansivity of I in their Theorem [3]...

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