{HEAD ~ The “cost} of {TAIL ~ survivability}” is defined as the ratio of the costs of network operation with and without survivability requirements 
of
{ HEAD ~ The “ cost } of { TAIL ~ survivability } ” is defined as the ratio of the costs of network operation with and without survivability requirements
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH