{HEAD ~ The top ply wall} is a single wall which is received within {TAIL ~ the bottom ply wall} 
{ HEAD ~ The top ply wall } is a single wall which is received within { TAIL ~ the bottom ply wall }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL