Primitive almost simple IBIS groups with sporadic socle

Abstract

An irredundant base $B$ for a permutation group $G\leq \mathrm{Sym}(\Omega)$ is an ordered subset of $\Omega$ with trivial stabiliser such that no base point is fixed by the stabiliser of its predecessors. Groups whose irredundant bases all have the same size are termed Irredundant Bases of Invariant Size (IBIS) groups, and were introduced by Cameron and Fon-Der-Flaass. In this paper, we contribute to the classification of primitive IBIS groups by classifying those that are almost simple with sporadic socle.