Editing Network theory (section)

===Network immunization===
The question of how to immunize efficiently scale free networks which represent realistic networks such as the Internet and social networks has been studied extensively. One such strategy is to immunize the largest  degree nodes, i.e., targeted (intentional) attacks<ref name="Callaway">{{cite journal | vauthors = Callaway DS, Newman ME, Strogatz SH, Watts DJ | title = Network robustness and fragility: percolation on random graphs | journal = Physical Review Letters | volume = 85 | issue = 25 | pages = 5468–5471 | date = December 2000 | pmid = 11136023 | doi = 10.1103/PhysRevLett.85.5468 | bibcode = 2000PhRvL..85.5468C | arxiv = cond-mat/0007300 | s2cid = 2325768 }}</ref> since for this case <math>pc</math> is relatively high and fewer nodes are needed to be immunized. 
However, in most realistic networks the global structure is not available and the  largest degree nodes are unknown.