When {HEAD ~ the bottom ply} includes {TAIL ~ two walls} , the top and bottom ply walls are offset from each other so that they mesh with each other 
includes
When { HEAD ~ the bottom ply } includes { TAIL ~ two walls } , the top and bottom ply walls are offset from each other so that they mesh with each other
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH