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On countable families of sets without the Baire property

Mats Aigner, Vitalij A. Chatyrko, Venuste Nyagahakwa (2013)

Colloquium Mathematicae

We suggest a method of constructing decompositions of a topological space X having an open subset homeomorphic to the space (ℝⁿ,τ), where n is an integer ≥ 1 and τ is any admissible extension of the Euclidean topology of ℝⁿ (in particular, X can be a finite-dimensional separable metrizable manifold), into a countable family ℱ of sets (dense in X and zero-dimensional in the case of manifolds) such that the union of each non-empty proper subfamily of ℱ does not have the Baire property in X.

On open maps of Borel sets

A. Ostrovsky (1995)

Fundamenta Mathematicae

We answer in the affirmative [Th. 3 or Corollary 1] the question of L. V. Keldysh [5, p. 648]: can every Borel set X lying in the space of irrational numbers ℙ not G δ · F σ and of the second category in itself be mapped onto an arbitrary analytic set Y ⊂ ℙ of the second category in itself by an open map? Note that under a space of the second category in itself Keldysh understood a Baire space. The answer to the question as stated is negative if X is Baire but Y is not Baire.

On p -closed spaces.

Dontchev, Julian, Ganster, Maximilian, Noiri, Takashi (2000)

International Journal of Mathematics and Mathematical Sciences

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