Therefore, when a given symbol of {HEAD ~ interest} is considered, the other symbols of interest may be considered as {TAIL ~ interfering symbols} 
Therefore , when a given symbol of { HEAD ~ interest } is considered , the other symbols of interest may be considered as { TAIL ~ interfering symbols }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL