The Baire Category of Subsequences and Permutations which preserve Limit Points

preprint2020arXivOpen access

Abstract

Let I\mathcal{I} be a meager ideal on N\mathbf{N}. We show that if xx is a sequence with values in a separable metric space then the set of subsequences [resp. permutations] of xx which preserve the set of I\mathcal{I}-cluster points of xx is topologically large if and only if every ordinary limit point of xx is also an I\mathcal{I}-cluster point of xx. The analogue statement fails for all maximal ideals. This extends the main results in [Topology Appl. \textbf{263} (2019), 221--229]. As an application, if xx is a sequence with values in a first countable compact space which is I\mathcal{I}-convergent to ℓ\ell, then the set of subsequences [resp. permutations] which are I\mathcal{I}-convergent to ℓ\ell is topologically large if and only if xx is convergent to ℓ\ell in the ordinary sense. Analogous results hold for I\mathcal{I}-limit points, provided I\mathcal{I} is an analytic P-ideal.

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