6,494 research outputs found
Connectedness and compactness on standard sets
We present a nonstandard characterization of connected compact sets. (C) 2010 WILEY-VCH Verlag GmbH & Co KGaA. WeinheimCEOCFCTFEDER/POCI 201
Connectedness modulo an ideal
For a topological space and an ideal of subsets of we
introduce the notion of connectedness modulo . This notion of
connectedness naturally generalizes the notion of connectedness in its usual
sense. In the case when is completely regular, we introduce a subspace
of the Stone--\v{C}ech compactification of
, such that connectedness modulo is equivalent to
connectedness of . In particular, we
prove that when is the ideal generated by the collection of all
open subspaces of with pseudocompact closure, then is connected modulo
if and only if is connected, and when is normal and is the ideal
generated by the collection of all closed realcompact subspaces of , then
is connected modulo if and only if is connected. Here is the Hewitt
realcompactification of .Comment: 28 page
Connectedness modulo a topological property
Let be a topological property. We say that a space is
-connected if there exists no pair and of disjoint
cozero-sets of with non- closure such that the remainder
is contained in a cozero-set of with
closure. If is taken to be "being empty" then -connectedness coincides with connectedness in its usual sense. We
characterize completely regular -connected spaces, with
subject to some mild requirements. Then, we study conditions
under which unions of -connected subspaces of a space are
-connected. Also, we study classes of mappings which preserve
-connectedness. We conclude with a detailed study of the special
case in which is pseudocompactness. In particular, when
is pseudocompactness, we prove that a completely regular space
is -connected if and only if is connected, and that -connectedness is
preserved under perfect open continuous surjections. We leave some problems
open.Comment: 12 page
The connected Vietoris powerlocale
The connected Vietoris powerlocale is defined as a strong monad Vc on the category of locales. VcX is a sublocale of Johnstone's Vietoris powerlocale VX, a localic analogue of the Vietoris hyperspace, and its points correspond to the weakly semifitted sublocales of X that are “strongly connected”. A product map ×:VcX×VcY→Vc(X×Y) shows that the product of two strongly connected sublocales is strongly connected. If X is locally connected then VcX is overt. For the localic completion of a generalized metric space Y, the points of are certain Cauchy filters of formal balls for the finite power set with respect to a Vietoris metric. \ud
Application to the point-free real line gives a choice-free constructive version of the Intermediate Value Theorem and Rolle's Theorem. \ud
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The work is topos-valid (assuming natural numbers object). Vc is a geometric constructio
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