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Hayek is widely recognised for having introduced the time dimension to the equilibrium construction and for his key role in helping inspire the fields of growth theory, information economics, and the theory of spontaneous order. The "informal" economics presented in Milton Friedman's massively influential popular work Free to Choose (1980), is explicitly Hayekian in its account of the price system as a system for transmitting and co-ordinating knowledge. This can be explained by the fact that Friedman taught Hayek's famous paper "The Use of Knowledge in Society" (1945) in his graduate seminars.

Whose 1980 book mentions "informal" economics?
Milton Friedman's