In {TAIL ~ addition}, links can be added to the network topology model to reduce the cost of {HEAD ~ network operation} 
In { TAIL ~ addition } , links can be added to the network topology model to reduce the cost of { HEAD ~ network operation }
OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD