a plurality of {HEAD ~ window system processing means}, one of which can refresh a graphic display by producing graphic display data based on {TAIL ~ original data} for the graphic display 
a plurality of { HEAD ~ window system processing means } , one of which can refresh a graphic display by producing graphic display data based on { TAIL ~ original data } for the graphic display
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH