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| Main Authors: | , |
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| Format: | Preprint |
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2025
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| Online Access: | https://arxiv.org/abs/2507.12929 |
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| _version_ | 1866911061288943616 |
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| author | Comerford, Mark Sumi, Hiroki |
| author_facet | Comerford, Mark Sumi, Hiroki |
| contents | Hereditarily non uniformly perfect (HNUP) sets were introduced by Stankewitz, Sugawa, and Sumi in \cite{SSS} who gave several examples of such sets based on Cantor set-like constructions using nested intervals. For non-autonomous iteration where one considers compositions of polynomials from a sequence which is in general allowed to vary, the Julia set is uniformly perfect for all sequences with suitably bounded coefficients, while Comerford, Stankewitz and Sumi showed in \cite{CSS} that for certain sequences of polynomials with unbounded coefficients, it is possible to have Julia sets which are HNUP. In this manuscript we give an example of a non-autonomous polynomial sequences whose Julia sets lie in between these two extremes in that they are not uniformly perfect, but also not HNUP. In addition we show that these Julia sets can be expressed as a `thick-thin' decomposition consisting of a ${\mathrm F}_σ$ subset which is a countable union of uniformly perfect sets and a ${\mathrm G}_δ$ subset which is HNUP. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_12929 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Thick-Thin non-Autonomous Julia Sets Comerford, Mark Sumi, Hiroki Dynamical Systems Primary: 30D05, Secondary: 28A80 Hereditarily non uniformly perfect (HNUP) sets were introduced by Stankewitz, Sugawa, and Sumi in \cite{SSS} who gave several examples of such sets based on Cantor set-like constructions using nested intervals. For non-autonomous iteration where one considers compositions of polynomials from a sequence which is in general allowed to vary, the Julia set is uniformly perfect for all sequences with suitably bounded coefficients, while Comerford, Stankewitz and Sumi showed in \cite{CSS} that for certain sequences of polynomials with unbounded coefficients, it is possible to have Julia sets which are HNUP. In this manuscript we give an example of a non-autonomous polynomial sequences whose Julia sets lie in between these two extremes in that they are not uniformly perfect, but also not HNUP. In addition we show that these Julia sets can be expressed as a `thick-thin' decomposition consisting of a ${\mathrm F}_σ$ subset which is a countable union of uniformly perfect sets and a ${\mathrm G}_δ$ subset which is HNUP. |
| title | Thick-Thin non-Autonomous Julia Sets |
| topic | Dynamical Systems Primary: 30D05, Secondary: 28A80 |
| url | https://arxiv.org/abs/2507.12929 |