A priority vector for the combination of {HEAD ~ requesters} has {TAIL ~ a sequential list} of requester identifiers 
A priority vector for the combination of { HEAD ~ requesters } has { TAIL ~ a sequential list } of requester identifiers
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH