One or more of {HEAD ~ the conducting layers} 50, 52 may be comprised of {TAIL ~ multiple materials} 
One or more of { HEAD ~ the conducting layers } 50 , 52 may be comprised of { TAIL ~ multiple materials }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL