منابع مشابه
A Collection of Dendroids
An uncountable collection of uniformly arcwise connected plane Suslinian dendroids is constructed which shows that the negations of the following properties: local connectedness, smoothness, pointwise smoothness, hereditary contractibility, and selectibility are not countable in this class of
متن کاملBottlenecks in Dendroids
A subcontinuum C of a dendroid X is a bottleneck if it intersects every arc connecting two nonempty open subsets of X. We prove that every dendroid has a point p contained in arbitrarily small bottlenecks. Moreover, every plane dendroid contains a single point bottleneck. This implies, for instance, that each map from an indecomposable continuum into a plane dendroid must have an uncountable po...
متن کاملMapping Chainable Continua onto Dendroids
We prove that every chainable continuum can be mapped into a dendroid such that all point-inverses consist of at most three points. In particular, it follows that there exists a finite-to-one map from a hereditarily indecomposable continuum (the pseudoarc) onto hereditarily decomposable continuum. This answers a question by J. Krasinkiewicz.
متن کاملOn contractible curves on normal surfaces
We give characterizations of contractible curves on proper normal algebraic surfaces in terms of complementary Weil divisors. From this we obtain some generalizations of the classical criteria for contractibility of Castelnuovo and Artin. Furthermore, we will derive a finiteness result on homogeneous spectra defined by Weil divisors on proper normal algebraic surfaces.
متن کاملA Stably Contractible C*-algebra Which Is Not Contractible
We exhibit a separable commutative C*-algebra A such that A⊗K is homotopy equivalent to zero, without Mn(A) being so for any n ≥ 1.
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ژورنال
عنوان ژورنال: Colloquium Mathematicum
سال: 1972
ISSN: 0010-1354,1730-6302
DOI: 10.4064/cm-25-1-89-98