This paper describes a complex of related ideas, ranging from Urbanik’s
-algebras,
through Deza’s
geometric groups and Zilber’s
homogeneous geometries, to Sims’
bases for permutation groups and their use in defining “size” parameters on
finite groups, with a brief look at Cherlin’s
relational complexity. It is not a
complete survey of any of these topics, but aims to describe the links between
them.