{HEAD ~ Neither the first input signal} nor the second input signal are applied to a base or {TAIL ~ gate} of the fourth transistor 
{ HEAD ~ Neither the first input signal } nor the second input signal are applied to a base or { TAIL ~ gate } of the fourth transistor
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH