  In this paper we study social exclusion in social (information) networks
using a game-theoretic approach, and study the stability of a certain class
community structures that are a Nash equilibrium. The main result of our
analysis shows that all stable community structures (Nash equilibria) in this
class are community structures under which some agents are socially excluded,
and do not belong to any of the communities. This result is quite striking as
it suggests that social exclusion might be the "norm" (an expected outcome) in
social networks, rather than an anomaly.
