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