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