1. The small world problem;Milgram;Psychol. Today.,1967
2. Collective dynamics of ‘small-world’ network;Watts;Nature,1998
3. Connected: The Surprising Power of Our Social Networks and How They Shape Our Lives—How Your Friends’ Friends’ Friends Affect Everything You Feel, Think, and Do;Christakis,2011
4. Emergence of scaling in random networks;Barabási;Science,1999