A p code frame or simply frame represents a unit of action or {HEAD ~ operation} in {TAIL ~ the system} 
in
A p code frame or simply frame represents a unit of action or { HEAD ~ operation } in { TAIL ~ the system }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL