Duality theory and long-period price theory

This paper concerns duality between long-period price systems in Sraffian models of production and the technologies of the various industries. We present a ‘principle of duality between prices and technique’ referred to a system of production, due to Bidard and Salvadori, and compare it with the usual textbook duality between cost and production functions, referred to firms\industries. We argue that the principle of duality for the system of production can be obtained, industry by industry, on the basis of the usual duality theory and that, in so doing, both ‘dualities’ are given a formulation more appropriate to firms/industries in long-period equilibrium.