"The full recognition of the general equilibrium concept can unmistakably be attributed to Walras (1874-1877), although many of the elements of the neoclassical system were worked out independently by W. Stanley Jevons and by Carl Menger. In Walras' analysis, the economic system is made up of households and firms. Each household owns a set of resources, commodities useful in production or consumption, including different kinds of labor. For any given set of prices a household has an income from the sale of its resources, and with this income it can choose among all alternative bundles of consumers’ goods whose cost, at the given prices, does not exceed its income. Thus, Walras saw the demand by households for any consumers’ good as a function of the prices of both consumers’ goods and resources. The firms were — at least in the earlier versions — assumed to be operating under fixed coefficients. Then the demand for consumers’ goods determined the demand for resources; and the combined assumptions of fixed coefficients and zero profits for a competitive system implied relations between the prices of consumers’ goods and of resources. An equilibrium set of prices, then, was a set such that supply and demand were equated on each market; under the assumption of fixed coefficients of production, or more generally of constant returns to scale, this amounted to equating supply and demand on the resource markets, with prices constrained to satisfy the zero-profit conditions for firms. Subsequent work of Walras, J. B. Clark, Wicksteed, and others generalized the assumptions about production to include alternative methods of production, as expressed in a production function. In this context, the prices of resources were determined by marginal productivity considerations."