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The extensible no-four-on-a-circle problem
Abstract
We show that there exists a set S ⊂ ℤ2 containing no four points on a circle or a line such that |S ∩ [n]2| = Ω(n) as n → ∞. Since any no-four-on-a-circle set in [n]2 has size O(n), this resolves (up to a constant) a question raised by the current authors and Keevash concerning the density of extensible no-four-on-a-circle constructions. Our construction is based on weighted random sampling from the integer lattice followed by careful deletion.
Related
BibTeX
@misc{ghosal2026extensible,
title = {{The extensible no-four-on-a-circle problem}},
author = {Anubhab Ghosal and Ritesh Goenka},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.20447},
eprint = {2609.20447},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.20447},
}
RIS
TY - UNPB
TI - The extensible no-four-on-a-circle problem
AU - Anubhab Ghosal
AU - Ritesh Goenka
PY - 2026
DA - 2026/09/17
PB - arXiv
DO - 10.48550/arxiv.2609.20447
UR - https://arxiv.org/abs/2609.20447
AB - We show that there exists a set S ⊂ ℤ^2 containing no four points on a circle or a line such that |S ∩ [n]^2| = Ω(n) as n → ∞. Since any no-four-on-a-circle set in [n]^2 has size O(n), this resolves (up to a constant) a question raised by the current authors and Keevash concerning the density of extensible no-four-on-a-circle constructions. Our construction is based on weighted random sampling from the integer lattice followed by careful deletion.
ER -