Correspondences
Mohammed Ali Khan · The New Palgrave Dictionary of Economics · 2008
Correspondences are versatile mathematical objects for which a rich theory can be developed. They arise naturally in many diverse areas of applied mathematics, including economic theory. For example, an individual consumer’s demand correspondence associates with each price system the set of utility maximizing consumption plans. Similarly, an individual producer’s supply correspondence associates with each price system the set of profit-maximizing production plans. These individual responses are correspondences rather than functions because of the constancy of marginal rates of substitution in consumption and in production over a range of commodity bundles.