And if Vc is initially too low, then {HEAD ~ less current} would flow through Q2 to increase {TAIL ~ Vc} 
And if Vc is initially too low , then { HEAD ~ less current } would flow through Q2 to increase { TAIL ~ Vc }
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL