Is selfishness always a bad thing, in the sense that people can only be better off when everyone is concerned with well-being of others as well as with his own, or are there situations in which altruis, can actually make things worse for all people involved? This paper tackles this question in...

We extend Kohlberg and Mertens' (1986) structure theorem concerning the Nash equilibrium correspondence to show that its graph is not only homeomorphic to the underlying space of games but that it is also unknotted. This is then shown to have some basic consequences for dynamics whose rest...