PreprintCC BY 4.0arXiv
The Siemons--Wagner property and Bradley's conjecture
Abstract
A transitive permutation group G≤Sym(Pcal) is said to have the Siemons--Wagner property ⋆3 if some three-point subset has a G-orbit longer than the orbit of every four-point subset containing it. In this paper we develop a structural theory of three-point orbits of finite $2$-transitive groups (orbit-length hierarchies, pointwise and setwise stabilizers, and their geometric realisations, including the unital and the ovoid), and we use it to completely settle Bradley's conjecture: a finite primitive group of degree at least $8$ satisfying ⋆3 is isomorphic to PSL(2,7) or PGL(2,7).
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BibTeX
@misc{zhang2026siemonswagner,
title = {{The Siemons--Wagner property and Bradley's conjecture}},
author = {Zhilin Zhang},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.24502},
eprint = {2610.24502},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.24502},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The Siemons--Wagner property and Bradley's conjecture
AU - Zhilin Zhang
PY - 2026
DA - 2026/10/17
PB - arXiv
DO - 10.48550/arxiv.2610.24502
UR - https://arxiv.org/abs/2610.24502
AB - A transitive permutation group G≤Sym(Pcal) is said to have the Siemons--Wagner property ⋆_3 if some three-point subset has a G-orbit longer than the orbit of every four-point subset containing it. In this paper we develop a structural theory of three-point orbits of finite $2$-transitive groups (orbit-length hierarchies, pointwise and setwise stabilizers, and their geometric realisations, including the unital and the ovoid), and we use it to completely settle Bradley's conjecture: a finite primitive group of degree at least $8$ satisfying ⋆_3 is isomorphic to PSL(2,7) or PGL(2,7).
ER -