Pith. sign in

REVIEW 4 cited by

Borel complexity of sets of ideal limit points

Not yet reviewed by Pith; the record is open.

This paper has not been read by Pith yet. Machine review is queued; the pith claim, tier, and objections will appear here once it completes.

SPECIMEN: schema-true, not a live event

T0 review · schema-true

One-sentence machine reading of the paper's core claim.

pith:XXXXXXXX · record.json · timestamp

arxiv 2411.10866 v2 pith:2RN7LYYS submitted 2024-11-16 math.GN math.CAmath.FA

classification math.GNmath.CAmath.FA
keywords mathcalmathscrsigmaidealidealslimitborelcombinatorial
verification ladder T0 review T1 audit T2 compute T3 formal
0 comments
abstract

Let $X$ be an uncountable Polish space and let $\mathcal{I}$ be an ideal on $\omega$. A point $\eta \in X$ is an $\mathcal{I}$-limit point of a sequence $(x_n)$ taking values in $X$ if there exists a subsequence $(x_{k_n})$ convergent to $\eta$ such that the set of indexes $\{k_n: n \in \omega\}\notin \mathcal{I}$. Denote by $\mathscr{L}(\mathcal{I})$ the family of subsets $S\subseteq X$ such that $S$ is the set of $\mathcal{I}$-limit points of some sequence taking values in $X$ or $S$ is empty. In this paper, we study the relationships between the topological complexity of ideals $\mathcal{I}$, their combinatorial properties, and the families of sets $\mathscr{L}(\mathcal{I})$ which can be attained. On the positive side, we provide several purely combinatorial (not dependind on the space $X$) characterizations of ideals $\mathcal{I}$ for the inclusions and the equalities between $\mathscr{L}(\mathcal{I})$ and the Borel classes $\Pi^0_1$, $\Sigma^0_2$, and $\Pi^0_3$. As a consequence, we prove that if $\mathcal{I}$ is a $\Pi^0_4$ ideal then exactly one of the following cases holds: $\mathscr{L}(\mathcal{I})=\Pi^0_1$ or $\mathscr{L}(\mathcal{I})=\Sigma^0_2$ or $\mathscr{L}(\mathcal{I})=\Sigma^1_1$ (however we do not have an example of a $\Pi^0_4$ ideal with $\mathscr{L}(\mathcal{I})=\Sigma^1_1$). In addition, we provide an explicit example of a coanalytic ideal $\mathcal{I}$ for which $\mathscr{L}(\mathcal{I})=\Sigma^1_1$. On the negative side, we show that there are no ideals $\mathcal{I}$ such that $\mathscr{L}(\mathcal{I})=\Pi^0_2$ or $\mathscr{L}(\mathcal{I})=\Sigma^0_3$. We conclude with several open questions.

Discussion (0). Continue with ORCID to comment.

Forward citations

Cited by 4 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Two $\mathfrak{b}$ or not two $\mathfrak{b}$?

    math.LO 2025-07 accept novelty 7.0 of 10

    The authors prove b(I) ≤ b_R(I) for every ideal I, characterize b_R(I) structurally, and show both numbers coincide for a range of definable ideals.

  2. On the complexity of upper frequently hypercyclic vectors

    math.FA 2025-06 conditional novelty 7.0 of 10

    The upper frequently hypercyclic vectors of a continuous linear operator always form a Gδσ set, and an explicit weighted shift shows they need not form a Gδ set.

  3. On generalized limits and ultrafilters

    math.FA 2025-05 conditional novelty 7.0 of 10

    Generalized limits with respect to an ideal are represented as averages of ultrafilter limits, with new characterizations of their diameter and differences.

  4. On maldistributed sequences and meager ideals

    math.GN 2025-05 accept novelty 7.0 of 10

    For ideals on omega, meagerness is equivalent to the Misik-Toth condition and to the comeagerness of the set of maldistributed sequences.

Pith tools