A generalization of a theorem of Hurewicz for quasi-Polish spaces

نویسنده

  • Matthew de Brecht
چکیده

We identify four countable topological spaces S2, S1, SD, and S0 which serve as canonical examples of topological spaces which fail to be quasi-Polish. These four spaces respectively correspond to the T2, T1, TD, and T0-separation axioms. S2 is the space of rationals, S1 is the natural numbers with the cofinite topology, SD is an infinite chain without a top element, and S0 is the set of finite sequences of natural numbers with the lower topology induced by the prefix ordering. Our main result is a generalization of Hurewicz’s theorem showing that a co-analytic subset of a quasi-Polish space is either quasi-Polish or else contains a countable Π02-subset homeomorphic to one of these four spaces.

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عنوان ژورنال:
  • CoRR

دوره abs/1711.09326  شماره 

صفحات  -

تاریخ انتشار 2017