Automorphism of incidence structure

Definition
An automorphism of an incidence structure is the following data:


 * A permutation on the point set
 * A permutation on the block set

such that a point and block are incident if and only if their images under the respective permutations are incident.

The set of automorphisms of an incidence structure form a group. This group is in fact a subgroup of the direct product of the symmetric group on the point set and the symmetric group on the block set.