{HEAD ~ a comparator} to compare {TAIL ~ the search key} to the entry determined to most likely be a match 
to compare
{ HEAD ~ a comparator } to compare { TAIL ~ the search key } to the entry determined to most likely be a match
HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH