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