Conway's groupoid and its relatives

TL;DR

This paper explores generalizations of Conway's 1997 construction of a highly symmetric permutation subset, called $M_{13}$, using combinatorial designs and hypergraphs, leading to new algebraic structures called Conway groupoids.

Contribution

It introduces and analyzes Conway groupoids as analogues of $M_{13}$ constructed from various combinatorial designs, expanding the understanding of these algebraic objects.

Findings

Conway groupoids can be constructed from different combinatorial designs.

These structures generalize the properties of the original $M_{13}$.

Open questions about their properties and applications are presented.

Abstract

In 1997, John Conway constructed a $6$-fold transitive subset $M_{13}$ of permutations on a set of size $13$ for which the subset fixing any given point was isomorphic to the Mathieu group $M_{12}$. The construction was via a "moving-counter puzzle" on the projective plane ${\rm PG}(2,3)$. We discuss consequences and generalisations of Conway's construction. In particular we explore how various designs and hypergraphs can be used instead of ${\rm PG}(2,3)$ to obtain interesting analogues of $M_{13}$; we refer to these analogues as Conway groupoids. A number of open questions are presented.