Editing Arrow–Debreu model (section)

=== Accounting for the existence of money ===
{{blockquote|No theory of money is offered here, and it is assumed that the economy works without the help of a good serving as medium of exchange.|Gérard Debreu|Theory of value: An axiomatic analysis of economic equilibrium (1959)|source=}}{{blockquote|To the pure theorist, at the present juncture the most interesting and challenging aspect of money is that it can find no place in an Arrow–Debreu economy. This circumstance should also be of considerable significance to macroeconomists, but it rarely is.|[[Frank Hahn]]|The foundations of monetary theory (1987)|source=}}Typically, economists consider the functions of money to be as a unit of account, store of value, medium of exchange, and standard of deferred payment. This is however incompatible with the Arrow–Debreu complete market described above. In the complete market, there is only a one-time transaction at the market "at the beginning of time". After that, households and producers merely execute their planned productions, consumptions, and deliveries of commodities until the end of time. Consequently, there is no use for storage of value or medium of exchange. This applies not just to the Arrow–Debreu complete market, but also to models (such as those with markets of contingent commodities and Arrow insurance contracts) that differ in form, but are mathematically equivalent to it.<ref>(Starr 2011) Exercise 20.15</ref>