In {TAIL ~ one embodiment}, {HEAD ~ the nodes} store data to track protection levels of their children nodes 
In
In { TAIL ~ one embodiment } , { HEAD ~ the nodes } store data to track protection levels of their children nodes
REL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH