A second separating unit contains {HEAD ~ a stack} of {TAIL ~ insert material}, one insert at a time being separated and pushed forward 
of
A second separating unit contains { HEAD ~ a stack } of { TAIL ~ insert material } , one insert at a time being separated and pushed forward
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH