Multiple headboxes could be controlled, such as when different headboxes are used to produce {HEAD ~ different layers} of {TAIL ~ a multi layer sheet} 
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Multiple headboxes could be controlled , such as when different headboxes are used to produce { HEAD ~ different layers } of { TAIL ~ a multi layer sheet }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL