The voltage at {HEAD ~ the function} of D1 and {TAIL ~ Q1} is a square wave 
of
The voltage at { HEAD ~ the function } of D1 and { TAIL ~ Q1 } is a square wave
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH