The paper investigates the conditions under which an abstractly given market game
will have the property that if there is a continuum of traders then every noncooperative
equilibrium is Walrasian. In other words, we look for a general axiomatization of
Cournots well-known result. Besides, some convexity, continuity, and nondegeneracy
hypothesis, the crucial axioms are: anonymity (i.e., the names of traders are irrelevant
to the market) and aggregation (i.e. the net trade received by a trader depends only
on his own action and the mean action of all traders). It is also shown that the
same axioms do not guarantee efficiency is there is only a finite number of traders.
Some examples are discussed and a notion of strict noncooperative equilibrium for
anonymous games is introduced.