Alternatively, the data can be stored in fixed locations and {HEAD ~ the portals} moved from location to {TAIL ~ location} 
moved to
Alternatively , the data can be stored in fixed locations and { HEAD ~ the portals } moved from location to { TAIL ~ location }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH REL TAIL TAIL TAIL TAIL TAIL