In {TAIL ~ a further variation}, the top ply includes inner an outer concentric walls, and the bottom ply can include {HEAD ~ one or two walls} 
In { TAIL ~ a further variation } , the top ply includes inner an outer concentric walls , and the bottom ply can include { HEAD ~ one or two walls }
OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD