{HEAD ~ the material} of {TAIL ~ said intermediate flat portions} and said corrugations having substantially the same thickness, 
{ HEAD ~ the material } of { TAIL ~ said intermediate flat portions } and said corrugations having substantially the same thickness ,
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH