Gérard Debreu Quote

L. Walras first formulated the state of the economic system at any point of time as the solution of a system of simultaneous equations representing the demand for goods by consumers, the supply of goods by producers and the equilibrium condition that supply equal demand on every market.

Arrow, Kenneth J., and Gerard Debreu. "Existence of an equilibrium for a competitive economy." Econometrica: Journal of the Econometric Society (1954): p. 265