Translation Universality and Countable Configuration Theory for Dense Gδ-Sets in Polish Abelian Groups
- 1School of Engineering, IT and Physical Sciences, Federation University Australia, P.O. Box 663, Ballarat, VI 3353, Australia
- 2Department of Mathematical and Physical Sciences, La Trobe University, Melbourne, VI 3086, Australia
Abstract
A dense Gδ subset of a Polish group is large in the sense of Baire category. We study a configuration consequence of this largeness. If G is a Polish abelian group, R⊆G is dense Gδ, and A⊆G is countable, then the set of translations {t∈G:A+t⊆R} is itself dense Gδ. Thus, every prescribed countable configuration occurs inside R in comeagrely many translated positions. We record labelled, affine, and difference consequences of this classical Baire category observation and relate them to the realization of Cantor configurations through Mycielski’s theorem. Combining the classical finite-arity theorem with an analytic preimage lemma gives a simultaneous analytic realization formulation. For any prescribed countable family of suitable real analytic maps and any dense Gδ target in the real line, there is a Cantor set on which all corresponding admissible analytic expressions simultaneously take values in the target. Repeated arguments are handled by restricting variable-identification maps to connected components on which they remain nonconstant. Applications are given to Diophantine approximation. In particular, Liouville and ultra-Liouville numbers exhibit the same countable translation universality despite their extreme metric smallness. More generally, approximation classes determined by arbitrary countable families of nonnegative rational approximation functions, each positive at infinitely many integers, are dense Gδ and inherit both the translation and analytic Cantor realization principles. The results emphasize the distinction between metric smallness and Baire category configuration largeness.
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BibTeX
@article{morris2026translation,
title = {{Translation Universality and Countable Configuration Theory for Dense Gδ-Sets in Polish Abelian Groups}},
author = {Sidney A. Morris},
journal = {Axioms},
year = {2026},
month = nov,
doi = {10.3390/axioms15110818},
url = {https://www.mdpi.com/2075-1680/15/11/818},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Translation Universality and Countable Configuration Theory for Dense Gδ-Sets in Polish Abelian Groups
AU - Sidney A. Morris
PY - 2026
DA - 2026/11/04
JO - Axioms
DO - 10.3390/axioms15110818
UR - https://www.mdpi.com/2075-1680/15/11/818
AB - A dense Gδ subset of a Polish group is large in the sense of Baire category. We study a configuration consequence of this largeness. If G is a Polish abelian group, R⊆G is dense Gδ, and A⊆G is countable, then the set of translations {t∈G:A+t⊆R} is itself dense Gδ. Thus, every prescribed countable configuration occurs inside R in comeagrely many translated positions. We record labelled, affine, and difference consequences of this classical Baire category observation and relate them to the realization of Cantor configurations through Mycielski’s theorem. Combining the classical finite-arity theorem with an analytic preimage lemma gives a simultaneous analytic realization formulation. For any prescribed countable family of suitable real analytic maps and any dense Gδ target in the real line, there is a Cantor set on which all corresponding admissible analytic expressions simultaneously take values in the target. Repeated arguments are handled by restricting variable-identification maps to connected components on which they remain nonconstant. Applications are given to Diophantine approximation. In particular, Liouville and ultra-Liouville numbers exhibit the same countable translation universality despite their extreme metric smallness. More generally, approximation classes determined by arbitrary countable families of nonnegative rational approximation functions, each positive at infinitely many integers, are dense Gδ and inherit both the translation and analytic Cantor realization principles. The results emphasize the distinction between metric smallness and Baire category configuration largeness.
SN - 2075-1680
ER -