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