{HEAD ~ The pair} of stacks is connected by a length of material which is folded on {TAIL ~ top} of the stacks 
{ HEAD ~ The pair } of stacks is connected by a length of material which is folded on { TAIL ~ top } of the stacks
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH