An arbitration method and mechanism assigning priority to one of {HEAD ~ a combination} of {TAIL ~ requesters} 
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An arbitration method and mechanism assigning priority to one of { HEAD ~ a combination } of { TAIL ~ requesters }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL