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