For each digital input signal, {HEAD ~ a pair} of {TAIL ~ references} is selected according to the state that represents the input signal 
of
For each digital input signal , { HEAD ~ a pair } of { TAIL ~ references } is selected according to the state that represents the input signal
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH