{TAIL ~ error} detecting {HEAD ~ means} for detecting an error in said feedback frame processed by said substituting means 
{ TAIL ~ error } detecting { HEAD ~ means } for detecting an error in said feedback frame processed by said substituting means
TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH