The universal covers of the sporadic semibiplanes (Q1815396)

The authors determine the universal covers of ten examples of flag-transitive \(c \cdot c^*\)-geometries (semibiplanes) which have an almost simple point-stabilizer. These universal covers were calculated before using coset-enumeration on a computer, but the present paper provides a computer-free proof. For this method, the flag-transitivity cannot be dispenced with. The authors use beautiful arguments, which work in all cases they consider. It seems to me that this method can be used at different places, but it might as well fail unexpectedly. In any case, the authors give conditions under which their method ``has a good chance to work''.