A E Lawrence wrote: > PAR PRI [S1,S2,...,Sn] > > where S1,S2,...,Sn are each sets of events. And events in Si take > priority over events in Sj when i>j. In effect, we have a partial order Ooopps i <j > relation with > > xi > xj when i >j for xi \in Si and xj \in Sj. i <j again, of course :-( Other E E O... Adrian -- Dr A E Lawrence (from home)