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