merging non redundant segments of the each of the related e mail messages into {HEAD ~ a single message document} by ordering {TAIL ~ the non redundant segments} hierarchically by the response level and the mail timestamp of the each of the related e mail messages 
by ordering
merging non redundant segments of the each of the related e mail messages into { HEAD ~ a single message document } by ordering { TAIL ~ the non redundant segments } hierarchically by the response level and the mail timestamp of the each of the related e mail messages
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH