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On the involution fixity of simple groups
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- Journal:
- Proceedings of the Edinburgh Mathematical Society / Volume 64 / Issue 2 / May 2021
- Published online by Cambridge University Press:
- 04 June 2021, pp. 408-426
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Let
$G$ be a finite permutation group of degree 
$n$ and let 
${\rm ifix}(G)$ be the involution fixity of 
$G$, which is the maximum number of fixed points of an involution. In this paper, we study the involution fixity of almost simple primitive groups whose socle 
$T$ is an alternating or sporadic group; our main result classifies the groups of this form with 
${\rm ifix}(T) \leqslant n^{4/9}$. This builds on earlier work of Burness and Thomas, who studied the case where 
$T$ is an exceptional group of Lie type, and it strengthens the bound 
${\rm ifix}(T) > n^{1/6}$ (with prescribed exceptions), which was proved by Liebeck and Shalev in 2015. A similar result for classical groups will be established in a sequel.
ON A PROBLEM OF PRAEGER AND SCHNEIDER
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- Journal:
- Bulletin of the Australian Mathematical Society / Volume 101 / Issue 1 / February 2020
- Published online by Cambridge University Press:
- 27 May 2019, pp. 80-87
- Print publication:
- February 2020
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This note provides an affirmative answer to Problem 2.6 of Praeger and Schneider [‘Group factorisations, uniform automorphisms, and permutation groups of simple diagonal type’, Israel J. Math. 228(2) (2018), 1001–1023]. We will build groups
$G$ (abelian, nonabelian and simple) for which there are two automorphisms 
$\unicode[STIX]{x1D6FC},\unicode[STIX]{x1D6FD}$ of 
$G$ such that the map is surjective.
$$\begin{eqnarray}T=T_{\unicode[STIX]{x1D6FC}}\times T_{\unicode[STIX]{x1D6FD}}:G\longrightarrow G\times G,\quad g\mapsto (g^{-1}g^{\unicode[STIX]{x1D6FC}},g^{-1}g^{\,\unicode[STIX]{x1D6FD}})\end{eqnarray}$$
