Article ID Journal Published Year Pages File Type
4657815 Topology and its Applications 2016 10 Pages PDF
Abstract

We show that the negation of each one of the following statements is consistent with ZF:(i) Every sequentially compact metric space X=(X,d)X=(X,d) is normal, i.e., the distance of any two disjoint non-empty closed subsets of X is strictly positive.(ii) If (X,d)(X,d) is a sequentially compact metric space then X is a UC space, i.e., every continuous real valued on X is uniformly continuous.(iii) If (X,d)(X,d) is a UC metric space then X is Lebesgue, i.e., every open cover of X has a Lebesgue number.(iv) If (X,d)(X,d) is a metric space such that every countable open cover of X has a Lebesgue number then X is Lebesgue.We also show:(v) For every metric space X, the following are equivalent:(1) Every sequence in X admits a Cauchy subsequence;(2) For every sequence (xn)n∈N(xn)n∈N of X, for each ε>0ε>0 there is an infinite Nε⊆NNε⊆N such that d(xn,xm)<εd(xn,xm)<ε whenever n,m∈Nεn,m∈Nε;(3) For every sequence (xn)n∈N(xn)n∈N of X, for each ε>0ε>0 and for each n0∈Nn0∈N there exist n,m∈Nn,m∈N, n,m≥n0n,m≥n0, n≠mn≠m such that d(xn,xm)<εd(xn,xm)<ε.(vi) The axiom of countable choice CAC implies that for every metric space X the following statements are equivalent:(1) X is Lebesgue;(2) Every countable open cover of X has a Lebesgue number;(3) X is UC.

Related Topics
Physical Sciences and Engineering Mathematics Geometry and Topology
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