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