  The quality of earthquake prediction is usually characterized by a
two-dimensional diagram 'n' vs. 'tau', where 'n' is the rate of
failures-to-predict and 'tau' is a characteristic of space- time alarm. Unlike
the time prediction case, the quantity 'tau' is not defined uniquely, so that
the properties of the (n,tau) diagram require a theoretical analysis, which is
the main goal of the present study. This note is based on a recent paper by
Molchan and Keilis-Borok in GJI, 173 (2008), 1012-1017.
