{HEAD ~ A relative positioning system} enabling {TAIL ~ a user} to return to a starting position or some other point on the users path 
enabling
{ HEAD ~ A relative positioning system } enabling { TAIL ~ a user } to return to a starting position or some other point on the users path
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH