Then, {HEAD ~ the output signal} is outputted by the output end of {TAIL ~ the buffer} 20; and 
Then , { HEAD ~ the output signal } is outputted by the output end of { TAIL ~ the buffer } 20 ; and
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH