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Striped structures of stable and unstable sets of expansive homeomorphisms and a theorem of K. Kuratowski on independent sets

Hisao Kato (1993)

Fundamenta Mathematicae

We investigate striped structures of stable and unstable sets of expansive homeomorphisms and continuum-wise expansive homeomorphisms. The following theorem is proved: if f : X → X is an expansive homeomorphism of a compact metric space X with dim X > 0, then the decompositions W S ( x ) | x X and W ( u ) ( x ) | x X of X into stable and unstable sets of f respectively are uncountable, and moreover there is σ (= s or u) and ϱ > 0 such that there is a Cantor set C in X with the property that for each x ∈ C, W σ ( x ) contains a nondegenerate...

Subcontinua of inverse limit spaces of unimodal maps

Karen Brucks, Henk Bruin (1999)

Fundamenta Mathematicae

We discuss the inverse limit spaces of unimodal interval maps as topological spaces. Based on the combinatorial properties of the unimodal maps, properties of the subcontinua of the inverse limit spaces are studied. Among other results, we give combinatorial conditions for an inverse limit space to have only arc+ray subcontinua as proper (non-trivial) subcontinua. Also, maps are constructed whose inverse limit spaces have the inverse limit spaces of a prescribed set of periodic unimodal maps as...

Subgroups and products of -factorizable P -groups

Constancio Hernández, Mihail G. Tkachenko (2004)

Commentationes Mathematicae Universitatis Carolinae

We show that every subgroup of an -factorizable abelian P -group is topologically isomorphic to a closed subgroup of another -factorizable abelian P -group. This implies that closed subgroups of -factorizable P -groups are not necessarily -factorizable. We also prove that if a Hausdorff space Y of countable pseudocharacter is a continuous image of a product X = i I X i of P -spaces and the space X is pseudo- ω 1 -compact, then n w ( Y ) 0 . In particular, direct products of -factorizable P -groups are -factorizable and...

Subgroups of -factorizable groups

Constancio Hernández, Mihail G. Tkachenko (1998)

Commentationes Mathematicae Universitatis Carolinae

The properties of -factorizable groups and their subgroups are studied. We show that a locally compact group G is -factorizable if and only if G is σ -compact. It is proved that a subgroup H of an -factorizable group G is -factorizable if and only if H is z -embedded in G . Therefore, a subgroup of an -factorizable group need not be -factorizable, and we present a method for constructing non- -factorizable dense subgroups of a special class of -factorizable groups. Finally, we construct a closed...

Summable Family in a Commutative Group

Roland Coghetto (2015)

Formalized Mathematics

Hölzl et al. showed that it was possible to build “a generic theory of limits based on filters” in Isabelle/HOL [22], [7]. In this paper we present our formalization of this theory in Mizar [6]. First, we compare the notions of the limit of a family indexed by a directed set, or a sequence, in a metric space [30], a real normed linear space [29] and a linear topological space [14] with the concept of the limit of an image filter [16]. Then, following Bourbaki [9], [10] (TG.III, §5.1 Familles sommables...

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