In {TAIL ~ a tracking hierarchy} {HEAD ~ all the relations} between the relation nodes are known to the tracking system 
In
In { TAIL ~ a tracking hierarchy } { HEAD ~ all the relations } between the relation nodes are known to the tracking system
REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH