Each zone may store {HEAD ~ instant messaging information} for {TAIL ~ a subset} of the peers at locations in the zone indicated by hashes of identifiers of the peers in the instant messaging group 
for
Each zone may store { HEAD ~ instant messaging information } for { TAIL ~ a subset } of the peers at locations in the zone indicated by hashes of identifiers of the peers in the instant messaging group
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH