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