The first input signal is applied to a base or gate of {HEAD ~ the second transistor} with regard to {TAIL ~ said reference point} 
The first input signal is applied to a base or gate of { HEAD ~ the second transistor } with regard to { TAIL ~ said reference point }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL