# Mixed-strategy Nash equilibria

I didn't find in books, so I'm asking - Mixed-strategy Nash equilibria is always only one or doesn't exist for the one certain game? And I know that there can be several(and can not be at all) pure strategy Nash equilibria.

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Pure strategies can be seen as special cases of mixed strategies, in which some strategy is played with probability $1$. In a finite game, there is always at least on mixed strategy Nash equilibrium. This has been proven by John Nash.
There can be several, but not in degenerate $2\times 2$-bimatrix-games. –  Michael Greinecker May 13 '12 at 17:33