Diagrammatic Demonstration of the Cournot Equilibrium

This note further develops Ikema's (1990, 1991) diagrammatic demonstrati on of the Cournot-oligopoly equilibrium on the price- quantity plane. It is shown that Ikema's method can be used to illustrate the Stackelberg and Bertrand equilibria on the price- quantity plane. Furthermore, we algebraically derive the ``monopoly- equilibrium'' curve and show that the Cournot- oligopoly equilibrium is stable if the monopoly-equilibrium curves for all producers are upward sloping.