The computer program is modified while {HEAD ~ the computer program} is executed by {TAIL ~ the processor unit} 
is executed by
The computer program is modified while { HEAD ~ the computer program } is executed by { TAIL ~ the processor unit }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL