In {TAIL ~ addition}, a subtractor produces {HEAD ~ an error signal} by subtracting the output signal from the reference input signal 
In { TAIL ~ addition } , a subtractor produces { HEAD ~ an error signal } by subtracting the output signal from the reference input signal
OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH