A jacket is separated from {TAIL ~ the stack} and pushed forward onto an insert unit on {HEAD ~ a slightly lower level} 
A jacket is separated from { TAIL ~ the stack } and pushed forward onto an insert unit on { HEAD ~ a slightly lower level }
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD