If the cost is impossible to determine, {HEAD ~ use} of {TAIL ~ cost} per unit to minimize the number of hops may be useful 
of
If the cost is impossible to determine , { HEAD ~ use } of { TAIL ~ cost } per unit to minimize the number of hops may be useful
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH