Rolf Mantel and the Computability of General Equilibria: On the Origins of the Sonnenschein-Mantel-Debreu Theorem

General equilibrium theory (GET) took the entire edifice of economic theory by storm during the 1950s. Its elegant existence theorems, proved by, among others, Kenneth Arrow and Gerard Debreu (1954) and Lionel McKenzie (1959), provided a framework of analysis that made more precise and sound the main intuitions of the neoclassical school. An even more important consequence of these developments may be that they set a new and higher standard of mathematical sophistication in economics. A remarkable aspect of this new standard was its nonconstructive flavor, pretty much in consonance with the postwar predominance of Bourbakian mathematics. The central role of GET in economics as the backbone of the mainstream is still uncontested. But its primacy as an all-encompassing theory of economic phenomena was challenged at its very inception, because of its inability to yield proofs of uniqueness and stability of equilibria from general characterizations of preferences and technologies. This lack of results, however, did not shake the pervasive use of neoclassical frameworks in which a system of competitive prices was seen as embodying all the relevant information in the economy. This tranquilizing belief