On subcompactness and countable subcompactness of metrizable spaces in ZF

2021/02/22 by Keremedis, Kyriakos
#03E325 #54D30 #54E35 #54E45 #54E50 #FOS: Mathematics #General Topology (math.GN)

paper · doi:10.48550/arxiv.2102.11243

Abstract

We show in ZF that: (i) Every subcompact metrizable space is completely metrizable, and every completely metrizable space is countably subcompact. (ii) A metrizable space X=(X,T) is countably compact iff it is countably subcompact relative to T. (iii) For every metric space X=(X,d), X is compact iff it is subcompact relative to T. We also show: (iv) The negation of each of the statements, (a) every countably subcompact metrizable space is completely metrizable, (b) every countably subcompact metrizable space is subcompact, (c) every complete metrizable space is subcompact is relatively consistent with ZF.

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