Keynesian Equilibrium and Fix Price Equilibria

The recent development of macroeconomic models with fixed prices has shown the importance of considering the type of unemployment in the economy, since this determines the effects of economic policy decisions. These models differ from the Keynesian approach by the hypothesis of rigidity of all prices, by the fact that equilibrium results from a tatonnement on quantities, and by the behaviour of firms whose role is as passive as that of households : firms and households are symmetrically treated. The most active role is that of the auctioneer who instead of adjusting prices, adjusts quantities. Keynesian equilibrium is defined by "Aggregated Demand and Aggregate Supply Functions" and given an aggregate production function, it corresponds to a determined price level. But given fixed prices, there is generally no equality between production and aggregate supply and demand. I try to restore the non-symmetrical Keynesian view and I study the formation and the type of equilibrium expected by firms facing constraints which arise from aggregate demand and from aggregate supply when prices are fixed. The existence and uniqueness of such an equilibrium is guaranteed without convesity. And when the expectations of firms are exact (when they coincide with the effective demand for goods and the effective supply of labour by households), the expected equilibrium is a fixed price equilibrium in the usual sense, i.e. the asymmetrical approach gives the same result as the symmetrical one.