storing the protection level of {HEAD ~ each} of {TAIL ~ the children} of the non leaf nodes 
of
storing the protection level of { HEAD ~ each } of { TAIL ~ the children } of the non leaf nodes
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH