Rad HAZU, Matematičke znanosti, Vol. 21 (2017), 169-177.


Vlasta Matijević

Department of Mathematics, Faculty of Science, University of Split, 21 000 Split, Croatia
e-mail: vlasta@pmfst.hr

Abstract.   With every topological space X is associated its Čech system C(X)=(|N(U)|, [pUV], Cov(X)). It is well-known that the Čech system C(X) of X is an inverse system in the homotopy category HPol whose objects are polyhedra and morphisms are homotopy classes of continuous maps between polyhedra. We consider the following question posed by S. Mardešić. For a given Čech system (|N(U)|, [pUV], Cov(X)) of a space X, is it possible to select a member qUV ∈ [pUV] in each homotopy class [pUV] in such a way that the obtained system (|N(U)|, [qUV], Cov(X)) is an approximate system? We answer the question in the negative by proving that for each Hausdorff arc-like continuum X any such system (|N(U)|, [qUV], Cov(X)) is not an approximate system.

2010 Mathematics Subject Classification.   54B35, 18B30, 54D30.

Key words and phrases.   Inverse system, Čech system, approximate system, polyhedron, nerve of a covering, arc-like space, chainable space.

Full text (PDF) (free access)

DOI: http://doi.org/10.21857/9e31lh4nrm


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