THE EXACT SPREAD OF M23 IS 8064

Abstract. Let G be a nite group. We say that G has spread r if for any set of distinct non-trivial elements of G X := {x_1; : : : ; x_r}  G# there exists an element y ? G with the property that (xi; yi) = G for every 1  i  r. We say G has exact spread r if G has spread r but not r +1. The spreads of finite simple groups and their decorations have been much-studied since the concept was first introduced by Brenner and Wiegold in the mid 1970s. Despite this, the exact spread of very few finite groups, and in particular of the finite simple groups and their decorations, is known. Here we calculate the exact spread of the sporadic simple Mathieu group M_23, proving that it is equal to 8064. The precise value of the exact spread of a sporadic simple group is known in only one other case - the Mathieu group M_11.