"Reinhard Selten shared the 1994 Nobel Prize in economics with John Nash and john harsanyi “for their pioneering analysis of equilibria in the theory of non-cooperative games.” One problem with various Nash equilibria is that they are not always unique. Selten applied stronger conditions to reduce the number of possible equilibria and to eliminate equilibria that are unreasonable economically. In 1965 he introduced the concept of “subgame perfection,” his term for this winnowing down of possible equilibria. “At that time I did not suspect that it often would be quoted, almost exclusively for the definition of subgame perfectness,” Selten wrote in his Nobel autobiography."