A colleague saw the same model-calibrating the elasticity of demand facing a Cournot oligopolist as a function of the number of firms in the industry--described at the University of Chicago and at M.I.T. A Chicago economist derived the formula and said, "Look at how few firms you need to get close to infinite elasticities and perfect competition." An M.I.T. economist derived the same formula and said, "Look at how large n has to be before you get anywhere close to an infinite elasticity and perfect competition."
Matthew Rabin