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Meager composants of continua (Q306162)

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scientific article; zbMATH DE number 6620870
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Meager composants of continua
scientific article; zbMATH DE number 6620870

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    Meager composants of continua (English)
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    31 August 2016
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    meager composant
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    indecomposable continuum
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    non-Suslinian
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    tendril class
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    For a metric continuum \(X\) and a point \(p\) of \(X\), the meager composant of \(p\) in \(X\) is defined as the union of all nowhere dense subcontinua of \(X\) that contain \(p\). Meager composants were introduced by \textit{E. Pearl} (ed.) [Open problems in topology. II. Amsterdam: Elsevier (2007; Zbl 1158.54300)], where he call them tendril classes. Bellamy posed two problems (see Problems 24 and 25, p. 262):NEWLINENEWLINE(a) Is there a continuum \(X\) with a proper dense open tendril class?, andNEWLINENEWLINE(b) If every tendril class of a continuum \(X\) is dense, and \(X\) has more than one tendril class, is \(X\) necessarily indecomposable?NEWLINENEWLINEThe continuum \(X\) is hereditarily \(k\)-coherent if the intersection of every pair of subcontinua has at most \(k\) components.NEWLINENEWLINEIn the paper under review, the authors make a detailed study of meager composants in continua. Among the results they obtain we can mention:NEWLINENEWLINE(1) if \(X\) is hereditarily \(k\)-coherent and has a meager composant that is not closed, then it contains a nondegenerate indecomposable subcontinuum.NEWLINENEWLINE(2) there is a hereditarily decomposable continuum \(X\) that contains an uncountable number of meager composants each of which is dense.NEWLINENEWLINEThis gives a negative answer to Bellamy's problem (b).NEWLINENEWLINE(3) if \(X\) has a meager composant which is not closed, then \(X\) has an uncountable collection of pairwise disjoint nondegenerate subcontinua.NEWLINENEWLINEProblem (a) of Bellamy remains open.NEWLINENEWLINEAmong other interesting questions, the authors also include the following intriguing problem:NEWLINENEWLINEIs there a continuum \(X\) for which the cardinality of meager composants is bigger than one but less than the cardinality of the continuum?
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