A distributed index may be used to implement an instant messaging system in {HEAD ~ a group} of {TAIL ~ participating peers} 
of
A distributed index may be used to implement an instant messaging system in { HEAD ~ a group } of { TAIL ~ participating peers }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL