The computer readable storage medium 10, wherein {HEAD ~ the operation} is parameterized by {TAIL ~ an element type parameter} and a key type parameter 
The computer readable storage medium 10 , wherein { HEAD ~ the operation } is parameterized by { TAIL ~ an element type parameter } and a key type parameter
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH